Look here: dcemu.co.uk and scroll down a bit. The gp2x downloads will appear on the right side.
Usually people don't get how to rip the games correctly since the emulator only takes real .iso files. Try Cddissect. It should get the job done. It also rips your pcengine and sega megacd games. It creates a cue file for the mp3s and your can choose what quality the audio should be encoded in. I can't find the homepage right now so just use this link: download Here is the documentation but that stuff is also in the readme.
EDIT: I thought these were also on dl.openhandhelds.org but they are not. We should update the list.