I spent the last 30 minutes searching topics/threads to make sure this wasn't already posted, I couldn't find it, but if it has been, i'll promptly delete this post. 
I've only been using RPG Maker XP for about two weeks, but i've already got so many extra graphics and audio files, and different game projects etc. I got tired of importing/exporting or copying the files directly into my project directories. Yes, you can stick the files in the RGSS\Standard\Graphics directory, and every project will then have access to the files, but I wanted to keep the original RTP directories/files clean and seperate from anything I make or download. I noticed in RMXP under the pull down menu "Game" is an option for SelectRTP... and I figured it'd be so much easier to add my own files into a mini-RTP or whatever you wanna call it. You can do it too, and it's quite easy.
Have a directory setup with two folders in it, one for Audio and one for Graphics. In the "Audio" folder, have four subfolders called BGM, BGS, ME, SE. And in the "Graphics" folder, have fourteen subfoulders called Animations, Autotiles, Battlebacks, Characters, Fogs, Gameovers, Icons, Panoramas, Pictures, Tilesets, Titles, Transitions, and Windowskins.
I have mine located in my C:\Games\RMXP\Oscarr directory (the directory you put it in will be important later)
Now, open up Registry Editor (click Start button, click Run, typed regedit.exe in the box, hit run/enter). You should see five folders on the left, you want the third one, called HKEY_LOCAL_MACHINE, so click on it, then click on SOFTWARE, then scroll down to Enterbrain, click it, click on RGSS, click on RTP. Now on the right you'll see following:
Name Type Data
---------------------------------------------------
(Default) REG_SZ (value not set)
Standard REG_SZ C:\Program Files\RGSS\Standard\
The directory listed for Standard under Data may be different for you, depends on where you installed the files. Now what we want to do is add our own entry, so under Standard, right click with your mouse. Click New> then click String Value
It should appear under Standard now, with your cursor in the box and "New Value #1" highlighted, erase it and call it whatever you want (I named mine Oscarr, ya I know, not very original). Now that you have it named, right click on it, and select Modify. In the Data box put the base directory to where you stored you files earlier (remember I said that would be important to remember). So for me, I put in C:\Games\RMXP\Oscarr
Ok now close RegEdit. Switch back to RMXP and go to the pull down menu Game, then Select RTP... in the RTP 1: Box, it should say Standard (unless you've turned it off.) In the RTP 2: Box, it should say (None), click on that and change it to whatever you named your RTP in the RegEdit (for me, it was Oscarr).
That's it, now you have access in this project to all the files in C:\Games\RMXP\Oscarr (or wherever you put yours).
--------------------------------------------------------
The point of all this? You can keep going back to RegEdit and creating more RTP's (i'm sure there's a limit, but, I don't know how many). You can make specific RTP's for certain scenarios. One called "Oceanic" for example that would include a multitude of water/sea/ocean sounds, Tilesets, Sound Effects, etc etc, you get the idea.
Basically it just helps keep your stuff more organised but grouped to gather by category.
Hope this was helpful to someone,
Cheers
I've only been using RPG Maker XP for about two weeks, but i've already got so many extra graphics and audio files, and different game projects etc. I got tired of importing/exporting or copying the files directly into my project directories. Yes, you can stick the files in the RGSS\Standard\Graphics directory, and every project will then have access to the files, but I wanted to keep the original RTP directories/files clean and seperate from anything I make or download. I noticed in RMXP under the pull down menu "Game" is an option for SelectRTP... and I figured it'd be so much easier to add my own files into a mini-RTP or whatever you wanna call it. You can do it too, and it's quite easy.
Have a directory setup with two folders in it, one for Audio and one for Graphics. In the "Audio" folder, have four subfolders called BGM, BGS, ME, SE. And in the "Graphics" folder, have fourteen subfoulders called Animations, Autotiles, Battlebacks, Characters, Fogs, Gameovers, Icons, Panoramas, Pictures, Tilesets, Titles, Transitions, and Windowskins.
I have mine located in my C:\Games\RMXP\Oscarr directory (the directory you put it in will be important later)
Now, open up Registry Editor (click Start button, click Run, typed regedit.exe in the box, hit run/enter). You should see five folders on the left, you want the third one, called HKEY_LOCAL_MACHINE, so click on it, then click on SOFTWARE, then scroll down to Enterbrain, click it, click on RGSS, click on RTP. Now on the right you'll see following:
Name Type Data
---------------------------------------------------
(Default) REG_SZ (value not set)
Standard REG_SZ C:\Program Files\RGSS\Standard\
The directory listed for Standard under Data may be different for you, depends on where you installed the files. Now what we want to do is add our own entry, so under Standard, right click with your mouse. Click New> then click String Value
It should appear under Standard now, with your cursor in the box and "New Value #1" highlighted, erase it and call it whatever you want (I named mine Oscarr, ya I know, not very original). Now that you have it named, right click on it, and select Modify. In the Data box put the base directory to where you stored you files earlier (remember I said that would be important to remember). So for me, I put in C:\Games\RMXP\Oscarr
Ok now close RegEdit. Switch back to RMXP and go to the pull down menu Game, then Select RTP... in the RTP 1: Box, it should say Standard (unless you've turned it off.) In the RTP 2: Box, it should say (None), click on that and change it to whatever you named your RTP in the RegEdit (for me, it was Oscarr).
That's it, now you have access in this project to all the files in C:\Games\RMXP\Oscarr (or wherever you put yours).
--------------------------------------------------------
The point of all this? You can keep going back to RegEdit and creating more RTP's (i'm sure there's a limit, but, I don't know how many). You can make specific RTP's for certain scenarios. One called "Oceanic" for example that would include a multitude of water/sea/ocean sounds, Tilesets, Sound Effects, etc etc, you get the idea.
Basically it just helps keep your stuff more organised but grouped to gather by category.
Hope this was helpful to someone,
Cheers