Well the first thing you need to understand is backing up *everything* is nearly impossible, and if you could backup everything you'd actually end up with restoring your PC to the same state it's in right now. If that's what you actually want to do, because you're changing your hard drive, what you need is a program like Norton Ghost, which will make a perfect copy of your drive on a new one. The new drive can be plugged in and run seamlessly.
There are very few problems that can be fixed by formatting and reinstalling that can't be fixed without resorting to that extreme. Make sure you've pursued every other option before you do this.
If you're looking to fix problems, what you want to do is back up your personal information, saved files, documents, etc. You can't back up installed programs because of copy protection schemes and the fact that they are highly dependent on the registry, which will disappear when you reformat and reinstall. This unfortunately includes RMXP, although from what I'm told if you contact Enterbrain's tech support they will get you up and running again after a reinstall. While you can back up all or parts of your registry and import the backup into a clean registry, if you only take parts you're liable to miss some parts you need and importing a full registry is going to have a lot of unintended and unforeseen consequences. So basically, you don't want to do that.
So, what you want to do is:
1. back up all your saved files, personal data, etc.
You are going to find 95% of all of this in the /Documents and Settings/ folder on your main hard drive (usually C
. Everything that's on your Desktop or My Documents, along with most of your user data, your Internet Explorer favorites, and so on are found here. It's likely to be very large, you will probably need several GB of space to back it up to so if you have a DVD burner or external hard drive that's the best way to go.
To identify other important directories, first if you created any personally that were outside of My Documents you need to back those up obviously. Next try opening up each application that you use, creating a new document, and then clicking File->Save as... to see what directory it saves to by default (this won't always give you an answer but it usually helps). Back up all that stuff too. While you're at it, see if there's an option to back up your data inside each program; for instance you will want to back up your bookmarks from Firefox and your email, accounts, and addresses from your email program, then make sure you copy those backup files to whatever backup device you're using. This will hold true for any program that stores its data in a database, which often won't get picked back up automatically when you reinstall. Take note you are likely to lose all your saved passwords in your web browser too so be ready to deal with that.
Older games in particular like to put save files inside their directory in /Program Files/ on your hard drive instead of using Documents and Settings, so you'll want to dig around in there for any saved games that are important to you.
You'll need to be comfortable with the fact that you WILL lose some things, though. It's nearly impossible to find and/or remember everything you saved on your computer in the last year. Make sure you think up a list of the most important items that you can't afford to lose and find them ALL before you go ahead with the format.
2. Make a list of all the software you use and make sure you can either download it again for free or that you have the licensed installer either on disc or on your backup device. Make sure you have all the serial numbers or authorization keys or what have you. If it came preinstalled on your computer it should still be there when you install again, but if it's a subscription service like an antivirus you will likely need to reactivate your subscription which might involve some phone calls and futzing around with tech support.
3. Once you have everything backed up and are ready to lose anything you forgot, you are going to need to figure out how to do a clean install on your system. Either your PC came with a System Recovery disc, or a Windows XP disc, or it came with a special recovery partition (common especially in laptops). Locate your Windows XP key, it should be on a sticker somewhere on your computer or else on the documentation that came with your PC (though it really *should* be on your case).
YOU CAN'T REINSTALL WITHOUT IT BUT YOU CAN LOSE ALL YOUR CRAP BEFORE YOU FIGURE THAT OUT, SO MAKE SURE YOU HAVE IT. <- very important.
If you are using a Windows XP disc to reinstall you are going to need the drivers for all your hardware. These should have come on discs that came with your PC in this case, but you can download newer ones off the manufacturer's websites if you lost the disc or just want them to be up to date.
If you don't have a disc, you are going to reboot your computer and look for something that reads "Press F9 to start system recovery" or something similar to that. If you don't see anything like that, check the manual and see if it tells you how to do system recovery, or call tech support. Follow the on-screen instructions and if it asks you whether you want to format, or do a clean install, or whatever, tell it yes.
If you do have a disc, and it's a System Recovery disc or labeled something like that, you are going to pop it in and tell your PC to boot from cd. If you don't get the option, look on the initial screen for something that says "Press F12 to select boot device" or something like that and push the appropriate button, then select your CD/DVD drive. Once again, check the manual if you can't find it on screen. Follow the on screen instructions and choose the most destructive-sounding options, they often don't like to use technical terms like "format".
If you have an original Windows XP cd, follow the same steps as above. When you get to the part where it starts asking you questions, you will need to tell it you want to install windows xp now, then it will tell you there's an existing windows xp installation - tell it you want to overwrite that installation. Next it will ask you if you want to do a quick or full format, and possibly whether you want to do NTFS or FAT32. You want NTFS and a full format (quick format works fine too and is much faster but full format will ensure your old data is more completely deleted). From there follow the on-screen instructions and give it all the info it asks for.
4. Activate Windows XP. The first time you reboot after Windows reinstalls it will ask you to activate Windows. Depending on whether it managed to instal your network drivers yet, it may attempt to activate by internet. This won't work, you are going to need to activate by phone. Explain to the nice Indian guy that you just reinstalled Windows and you need to reactivate it, tell him you only have it installed on one computer, (or whatever, I'm not telling you to lie but he won't activate for you otherwise so...). Follow his directions, the whole thing takes about 5-10 minutes, everything should be fine.
6. If you used a system recovery disc or partition, you should be right back to the way the PC was when you got it and you can skip most of this step. With a Windows XP cd, you are going to need to install all your hardware drivers, which you should have if you followed instructions! It's actually okay to install them all at once without restarting each time like they ask you to 99.9% of the time, but it's best to do your motherboard drivers, then your video and sound drivers, then mouse drivers (your mouse works fine without them, they just add extra features). Don't install your network card drivers until after you install your antivirus if you want to save yourself a lot of possible grief. Then reboot.
Finally, you need to install any other peripherals like your printer, scanner, whatever. Reboot after you're done with that.
7. If you used a Windows XP disc or your computer didn't come with antivirus software and you're using your own, install that first (then install your network drivers if you skipped them before like I said to). Reboot after those two things. Reinstall all your other software. Bring something to do, like a book, this is going to take a while.
8. Copy all your stuff from your backup back to where it belongs. If, after copying your Documents and Settings over, your desktop and my documents and such don't show up, this is a result of you having used a different user name than before. Just go to Documents and Settings, find your old user name, and copy everything inside that folder to your new username folder. Don't forget to re-import all your email, firefox bookmarks, etc.
9. This is usually the part where you go "FUUUUCK I can't believe I forgot XXX, now I'm fucked!"
10. After you get through the grieving process, you're just about done
Disclaimer: I provide no warranty whatsoever on this post, it will work if you follow instructions correctly but I can't guarantee I've been clear enough or accurate enough to make sure that you will : DD
Good luck!
