Everyone get a virus scanner and keep it up to date.
Don't click random links or accept files from people unless you know they are going to send it.
Make your email password difficult.. 6 - 10 chars with numbers in it..
Bam - problem solved
If you have XP I would recommend getting Service Pack 2 as soon as possible.. IE6SP2 (Internet Explorer) is MUCH more secure and has a built pop-up blocker along with a "Add-on manager". IE used to allow software to be installed via an activex control... it now blocks this and alerts you, as well as all other things that try to install or run on your system.. It's much better (im actually using it more than firefox right now)
Good stuff:
Symantec Virus & Security checker (free)
Ad-Aware - find & remove adware/spyware/popup loaders/dialers
Firewall - Zonealarm (XP Users: Get SP2 and enable the firewall.. its better in SP2)