Your hardware selection looks good to me. With 4gb RAM, run Vista 64 Professional (if you can get it from work). I run it, and have never had problems.

Also, I only went with a Geforce 8800GT and it works great... and was only $220. If you have the money though, go with the card you stated.

Also, if you're into that kind of thing, get a big aftermarket CPU Heatsink/Fan. The Q6600 can overclock like a mofo. Just make sure your motherboard is overclocking friendly. I have a gigabyte motherboard and OC'ed my Q6600 to 3.0ghz. Also, if you go this route or ever intend to go this route, make sure that your Q6600 has "G0 Stepping".