For those of you interested in the PSP and getting the most from it, there is only one central download resource you need. it is called download.QJ.net and the PSP section can be found at:
http://dl.qj.net/PSP/catid/106
This is a great download site and it contains pretty much everything you ever need for PSP custom firmwares, emulation, homebrew and more.
The Firmwares section contains the custom firmware installers, plus all of the official Sony firmware releases (which are needed for the custom firmware installers to work).
The Emulators section contains pretty much all the useful emulators for the PSP, ranging from Amiga to SNES, Genesis, GBA and lots more systems.
And once you have a custom firmware on your PSP the homebrew sections are worth looking at too. The Homebrew games section contains some nice public domain games to try. I have been playing a few of them on my PSP for a long time.