If you check out PPT's graphics community on LJ (
http://www.pinkpt.com/forum/viewtopic.php?t=4130), you could join and have access to an amazing list of graphics resources compiled by Marissa. There are lots of places to download brushes for PSE and other versions.
About PSP brushes, I've heard you can change the .jbr to .abr, but it only works sometimes, for certain versions.