I love the fact that I searched "psp custom gameboot.prx" on google and the first result was :
View topic - gameboot .prx • Wii Brew - For All Your Wii Needs ...
wii.brewology.com/forum/viewtopic.php?f=69&t=19780 - Cached
3 posts - 3 authors - Last post: 22 Jul
Talk about anything and everything related to PSP Homebrew here. ... gameboot .prx. wouldn't it be cool if there were a plugin that changed ... I definitely remember custom gameboots or w/e they were called at the time. ...
This thread
Edit - try this :
http://forums.afterdawn.com/thread_view.cfm/347769