Wow.
Guys, I can't imagine reformatting every 6 months. How about running MS Antispyware and (after that's all done & you've rebooted and run it again to confirm it's all clean) MSCONFIG and letting us know what's running in the background?
What, particularly, is slow? You mention a 3D program - so what does Task Manager show is running (and using CPU time) when you run that application?