well, if u have two pci-e slot u can
That's what I thought.
+1you have a few options! sell your current gpu and buy ati, then when it comes time to upgrade again you can just go crossfire
or settle with your current gpu
or buy a single better performing gpu nvidia or ati!
dont worry i made the same mistake a while back, my aging 7950gt wasnt what it used to be so i sorced another and though i might aswell go sli until i realised my motherboard only supported crossfire