Hi, I hate to double post so I'll just
link to the one I made in Tinman's Easy Jailbreak thread.
A little deeper in, you'll also find an iPhysics fix if you use that app at all also.
Additionally, if you get a black screen and some really odd looking white text on the top of your screen, its because you don't have the GBA bios file thats required to run the emulator. A simple google search gba_bios.bin will sort things out. Drop that file into your /Applications/gpsphone.app folder and you're all set.