Hmm yea thats strange, you're setup is pretty good. The RAM will certainly help, although if the old RAM was slower the ballistix stick will default to the slower speeds of the old RAM, but 1Gig is good...
The only thing I can think of at the minute is, how much HD space you got left? And how long since you're last defrag? Also I've gotta mention the mandatory response of 'have you got the latest drivers?' hehe although you probably have.
