It will not work if you have a revision 0 card, not sure how many other ones there are but I am guessing the new ones will work, I downgraded my XPS gen 2 to a 6800 vanilla with bios version 05.41.02.29.a8.
It works a lot better than on the 7800gtx (all drivers work with it, works in the bios, works when windows is booting, or booting off cd's/linux console, etc.) however everything detects the card I got as single link (vs dual link with the 7800 gtx/ 6800 ultra, however those dont work right, and only two drivers versions will even run 1280x800 correctly. I am probably going to look for a rev. 01 card and test that, and maybe a rev. 02 as well, if they exhist, anyone know what all the revisions for the 6800 vanilla are?