Gtx 560 sli antialiasing problem

Hello all,
I have an issue with 2 games, black ops and cod5. I have 2 gtx 560ti's and a i5-2500k. My problem is both games play choppy when antialiasing is enabled at any setting. If i disable antialiasing the games play fine. This only does this under windows 7 I have windows xp installed on the same computer with no issues. Also if i disable sli then both games play fine even with antialiasing enabled. I've tried reinstalling drivers and windows. Any suggestions?