Ok, well the biggest thing with a PSP is its newest features that sony bring out and the ability to play home made games. This is achievable with Custom Firmware, the latest to date being 3.9x M33.
My sig below gives tutorials on downgrading and upgrading to custom firmware. If you let me know your firmware version, i can tell you your options.
Homebrew is home made apps, this also includes ISO's which are illegal copies of current PSP games. THis is all i have to say about ISO's as any further talk isnt allowed.
So yeah, lots of cool stuff, emulators (virtual consoles, like N64 on the psp), IR remotes, the list goes on and on.
Kev
