QUOTE(knight84 @ May 28 2007, 02:05 PM)
you can try using Avira Antivir Personal Classic
It's the best Free Antivirus around this time.
Low Memory Usage (lower than 10K)
Their Premium Edition won the best detection rate in
http://www.av-comparatives.org/check it out.
Con: Only virus protection
or
Clamwin with Winpooch
it's open source and it's free of course

Claim to be the best near future.
ClamWin Free Antivirus 0.90.2.1
ClamWin is a Free Antivirus for Microsoft Windows 98/Me/2000/XP/2003. It provides a graphical user interface to the Clam AntiVirus engine. It features a command line interface for scanning files, updating the virus definitions, and a daemon for faster scanning needed on high performance systems.
ClamWin Free Antivirus For Windows is a completely free and open source anti-virus software package. It uses the GNU General Public License by the Free Software Foundation.
Homepage -
http://www.clamwin.com/content/view/71/63/