One of the most common things I do with clients and friends computers is to remove the OEM pre-installed anti-virus and spyware. They are typically the worst culprits for a slow running computer. I normally install AVG Free Edition, ensure they have Windows Defender, and make sure the default Windows Firewall is on. I’ve also experimented with NOD32, which is really good, too.
What do you use for anti-virus + spyware protection, and why?