the great thing about rmxp is the ability to import custom graphics.
You can make 3d graphics, make them into 3d looking sprites then import it into rmxp for snazier graphics.
But there is no magic button that makes everything look nice, if that is what you are asking.
You would have to make the 3d sprites yourself.
What effect were you going for? True 3d? Or faux 3d?
Do you have screen shots of what you would like to achieve?