About all you can do is keep your computer free from spyware and virus's by using such programs as Spybot: Search & Destroy and Ad-Aware. also www.pc-cillin.com
is a website with a free virus scanner for your computer. Like jolancer said, RAM will only do so much. In your case you mainly need to keep the HD free of clutter and keep it defragged if you haven't done that in a while.