Can you but Pokemon FireRed on your r4 card?

yes you can

put you can't play it XD

if you have a 3-in1 pack (Expansion Cart) for the eazyflash (or however you write it) and then put the GBA ROM on the Expansion Cart and then you can play it with on your ds

oh one tip

don't buy a whole package only the Expansion Cart and download the firmware for the flhascard you need, delete the firmware from your R4 and put the firmware from the easyflash (what you downloaded for free) on the card