There is to be a high-end version released by Asus in May that will use 256mb GDDR3 memory and is rumored to use a PCI-e x16 slot. But that's just the high-end, as others have said, a PCI or PCI-e x1/x4 will work too.
This isnt SLI, it will be w/in a year till it is used. Not to mention on normal games its still taking a great deal off the cpu and gpu. It is well worth it even today.