Good Call and be advised
 

Good choices. XP is proven Vista is not. If your building your system try pricewatch or newegg they have the best prices on all pc components. Pricewatch is a website that basically monitors the web for prices on a specific product you select, it has no favorite store. A E6700 goes for around $315 online see how much you pay if you go to a retail store. Also the price difference between a 8800 GTX and 8800 Ultra is not much at all 10-40bucks!. Go with Ultra and savor the extra 63mhz core speed and the extra 260 mhz of memory speed. I am sure it will give you better performance for not much more $. I found that shopping online saved me $$$, so you can say im sharing the wealth.

One more bit of advice many will benefit from. I highly recommend you look into the Asus Striker Extreme or the ABIT IP35 Pro motherboard. Both are fast and are good overclockers, especially the abit.They both support the latest Intel dual core processor coming, the Penryn, which has a 1333mhz system bus. Based on a limited number of reviews out about Penryn, it smokes the current processor out there.

I have an Intel QX6700 quad core running Vista with no problem. THe biggest improvement you will see in the sim world will come from the 8800 Nvidia video card. It made a marked difference when I put SH4 on my new system. Everything loaded faster and moved much smoother. WOrd of advice, Haunt the Nvidia site as the Vista drivers for the 8800 are being updated on a regular basis.