hey i was using 1.48 and i thought most homebrewn games worked, but i tried carbie, wonkieguy, dangerousxmas, and nebulas but none of them worked. They all are .gba, i got them from the gba competitions.
Don't try to get something to work this soon. They are still releasing new versions every 3 days or so.
If you are lucky, a game might work a little, but you shouldn't expect to actually use that emu for playing GBA-Roms of any kind.
The games you mentioned have commercial quality and use a lot of tricky stuff as commercial games do. Don't think that GBA homebrewn can run easier just because it's homebrewn
Try to get previous versions of GPAdvance. Revision 1.43, or 1.46 should be ok. With SourceForge's "Browse CVS" interface, it's easy to get a previous version.
We're currently working on heavy changes within it, so current releases might be a unstable. Fortunately, this work should be finished soon.