Get on newegg.com and i believe you can do this fairly easily. I would get an AMD system to cut cost, you could probably get a 5000+ and 2gigs of ram, as well as a 8600gt. Always try to get the best parts possible, dont cut costs with power supplies, etc. or you will regret it. There are tons of deals on newegg.com that will meet your budget. Happy hunting!
Comes to $915 before shipping. This is a pretty decent case, used it for one of the grandkids build. PSU not great but would work and can always upgrade it later. I think you'd be better off with XP given the problems with Vista but regardless, get the OEM version