it doesnt seem to me like it would be worth investing more money into a 7yr old machine. if you have the money, start with a clean slate and get a completely new one.
however, i wouldnt get that velocity pc. even among custom pre-builts it doesnt look like a good deal. for nearly $1200 you only get a 9800gt whereas a rig like this example
iBUYPOWER Computer :: Gamer Paladin E750
is not only cheaper, but comes with a MUCH faster hd 5850.
ofcourse in the best possible case, you could build it yourself instead paying to get it built for you and youd get more for your money.