I have an HD 4870 x2 in my i7 920, Asus P6T Deluxe computer that has worked will with both XP and Vista. I upgraded to Win 7 Ultimate and it now crashes on every attempt to install and tweek. After troubleshooting for some time, I ended up putting an antiquated X1900 I had and it works perfectly. I am not willing to rule out Windows being the issue and would like some advice or insight as to what could be the problem. I have read several articles stating that Win 7 has had issues with Crossfire and 2 GPU vidio cards from ATI....is there a known fix?
If the card loads up fine in the BIOS screen, and shows an image before you try to install the ATI drivers (if it runs fine in VGA mode that is), I'd blame Win 7. I don't have a solution for you if that's the case though since I don't have one of those cards, but maybe you feel better if some-one else thinks it's Win 7s fault :-)