To answer your question, yes it can be done.
Any modded Xbox can emulate GBA. I believe the Big Ass Emulator Disc # 2 or #3 has the emulator and roms on it. My brother, thaddius, downloaded it the other day and we played it a while.
You can also look around for Emulators for xbox and you can of course put roms on there too. They generally have instructions on their site and stuff.
Good luck.