the memory type of the gpu is not dependent on the motherboard (unlike your ram for the board)
there are only a few things to consider, first is the slot, if it's AGP then the card should also be AGP, pci-e card for pci-e slot (board).
next is psu, it is recommended to use good quality psu. for powerful GPU's you will need good psu's also.
that's about it
i had a athlon x2 5200 overclocked and it had trouble playing bf3 with my old 512mb card. it could have been just the card but it may be a bottleneck to a better card. i believe i tried my 550ti vs my new rig and it had bad frame rate drops as well, but it could have been due to the fact i dont have more than 2gb of ram in that system since my other slots are shot causing blue screeing. with 3gb it ran better.