Think I had a virus or trojan

Ooops, I guess I wasn't clear, ha ha! No, the creator of CCleaner originally called it "Crap Cleaner." I read this in an industry magazine. The publishers changed the name to "Cruft Cleaner" then it was eventually shortened to CCleaner. It's certainly not crap, but will clean the crap off of your system, get it? I recommend CCleaner.

As for Norton360, if you are comfortable with the product, why switch. Some of the free products (Avira comes to mind) will show pop ups for the paid versions (which basically removes the popup). I'd pay just to avoid that.

If your PC is seven years old, I'd certainly upgrade to 7 with the purchase of a new PC, and not install it on the one you have. I'm guessing 7 home premium (or whatever they call it now) retails for $120 - $180. I'm also guessing a basic but decent new system can be had in the $500 range for a desktop, add 50% for a notebook. It's kind of a big chunk of the cost, and you won't notice all the nice features (such as Aero) if your hardware doesn't support it. 7 years is a pretty good run for a PC. In my organization, we switch out laptops every three years, workstation PCs and servers every five.