Basic Protection

Spy ware, Anti-Virus

Install Spybot S&D and update the definitions regularly.

In Spybot S&D go to Immunize and move down to the Enable permanent blocking area and insure the drop down is set for Block all pages silently.

Install the prevention protection below and help your friends from being infected on the Internet.

"An ounce of prevention is worth a pound of cure."

Install the prevention protection on ALL User Account IDs.

Empty the Recycle Bin frequently.

Run CleanUp! as the Temp folders should be cleaned out periodically as installation programs and hijack programs leave a lot of junk there.
http://cleanup.stevengould.org/
Then reboot to let it clean out what it found.

By the way, in order to improve Internet Explorer (IE) performance the Temporary(TIF)should be cleaned out periodically.
Also, it is a good idea to limit the size of the TIF to 200MB for performance sake.
In IE go to Tools then Internet Options then Settings and move the slider down to 200MB.

You should install Windows Service Pack 2 and ALL Critical Updates to help from being continually infected.
In Internet Explorer go to Tools then Windows Updates and install each patch one by one rebooting when necessary.