I have a new Dell that I got a few months ago. It's a 3.0 with a Gig of RAM and a 160 GB HD.
I have XP home with SP2.
When I first got it I would open any application, like Word and it was almost instant. Over the past few months that I;ve had it it seemed to open slower.
I have Norton installed and run the virus checker regularly, I also run Spybot and Ad-aware weekly.