What do I need to play gba on r4?

I just ordered a R4 from dealextreme and I was wondering what I could buy for slot-2 to play gba roms?

You wasted your money by getting an R4, just letting you know. It's work, sure, but pretty much every other device on the market is superior at this point.

For GBA homebrew (please read the DCEmu rules), the EZ-Flash 3in1 will work. You'll use a homebrew app called GBA ExpLoader to load games from your slot-1 microSD card to the 3in1 and launch them.

Nothing, as the above member said, you wadted your money, besides, the Nintendo DS cannot play GBA from slot1 EVER, its like the same thing as playing n64 on DS, maybe now that DSi is out with a new proccessor nd 16mb of ram it could work.