I've heard of people making games for a gameboy using blitz. How do you do this for a gameboy advance and/or DS?
Thanks!
You can't.
(You could prototype with them, though).
Your best bet is to learn C and a bit of hardware stuff and use DevKitPro. (Or, if you want something easier, you can use PALib for DS and there's a few GBA BASICs out there).