You state you have a DSi. GBA games CANNOT be run on ANY DS without some form of slot2 cart. Since the DSi has no slot2, it it NOT possible to run GBA games on it. Your only hope is that Nintendo will someday make some GBA games available through their DSiWare.
This is probably the most asked question on GBAtemp and it has been answered many times. This thread will now be closed as redundant.