FOR ALL N00BS THAT WISH TO PLAY GBA GAMES ON THEIR SLOT-1 CART:
A) If you are using a DS LITE or DS FAT (WITH THE GBA SLOT) just go get a EZ-Flash 3-in-1.
B) If you are using a DSi or later pickup the iPlayerDS flashcard as there is currently a homebrew application that allows you to play GBA Games in 99.99% quality. There are still some games that have problems. I'm still kicking myself for not participating in Tempmas 2009 for a chance to get the iPlayerDS cart.
C) If you are using a DSi and don't want to get an iPlayer DS then just wait for the DSi Ware to become hacked and then wait for a GBA Loader for the DSi. I am confident that this is possible but it will take some time to be perfected.