all your opinions aside fellas- Vista IS the better choice for gamers- regardless of what you've tried in the PAST it HAS been updated and provides superb protection and no longer has the problems when it first came out with games.
Since your building a high performance computer... iam wondering why it's in this section.... a budget of 1500 dollars can build you a near state of the art gaming machine... and you have 2000 dollar budget...
Vista Home Premium -or- Ultimate edition are the only 2 ever reccomended for gamers- ultimate has some extra saftey things and data encryption and the like but may never go to use for you personally- so look into the changes and decide for yourself.
As for the nay sayers believing that Vista never plays games well - with 2gb or more of RAM it plays everything just fine. With the large budget you have you can get a nice 4GB RAM and have vista running everything for its pretty new look- and still never worry about your games using RAM.
Get some nice fast Harddrives, the Ultra card, and a q6600 from intel and your set - even without overclocking, at least that's what I would do with 2,000 if i had it.
and Sli really isn't worth it yet- you pay double (2 cards) for about a 43% performance gain, and that % IS based on which cards you get- Sli 2 ultras- not worth it at all- almost no gain. Wait until future Sli comes out.
and yes 2 8800GT in true SLI will outperform and ultra.. but why wouldn't it? its 2 cards... if you wanna fight that.. why not spend a little more or wait for the new cards to come out and Sli them? they'll beat the ultra too.