If you have all the updates for Vista and the right hardware, you shouldn't have any problems. My hardware is much like yours (I only spent about $550 when I upgraded to Vista to ensure it was good stuff).
My Vista box has been stable for months (only rebooted once due to a power outage in 4+ Months). I use it to do all sorts of crap, including
EU, virtual machines for multiple development environments, web browsing (to some places that are not exactly safe, either), and I stress it at 100% (2 Cores) with BOINC -- 24/7. It also has a business intelligence server, licensing servelets, and office API development stuff.
I know not all Vista machines have a great reputation, but I have *NEVER* been able to throw this much crap at any machine before. It took me less than an hour to make OS/2 Warp cry for help (way, way, back), but Vista ROCKS when you have the right hardware and configuration!
Good Luck figuring it out -- I would visit dslreports.com and see if perhaps you have excessive packet loss (or other network/bandwidth issues).
Oh, and I've found that with my 6 MBit cable connection, setting the
EU bandwidth parameters to ~ 1 MBit was better than shooting too high, performance-wise.