Brian's advice re avast is spot on...
Free antivirus - avast! 4 Home Edition
http://www.avast.com/eng/avast_4_home.html
(Choose Custom Installation and under Resident
Protection, uncheck: Internet Mail and Outlook/Exchange.)
...but stay away from PFW
PFW Criticism.
http://en.wikipedia.org/wiki/Personal_firewall#Criticisms
"Personal Firewalls" are mostly snake-oil.
http://www.samspade.org/d/firewalls.html
Why your firewall sucks.
http://tooleaky.zensoft.com/
"But I quickly realized the truth: The added protection provided by
outbound filtering is entirely illusory."
At Least This Snake Oil Is Free.
http://msinfluentials.com/blogs/jesper/archive/2007/07/19/at-least-this-snake-oil-is-free.aspx
Deconstructing Common Security Myths.
http://www.microsoft.com/technet/technetmag/issues/2006/05/SecurityMyths/default.aspx
Scroll down to:
"Myth: Host-Based Firewalls Must Filter Outbound Traffic to be Safe."
Activate and utilize the Win XP SP2 built-in Firewall; Uncheck *all*
Programs and Services under the Exception tab.
Read through:
Understanding Windows Firewall.
http://www.microsoft.com/windowsxp/using/security/internet/sp2_wfintro.mspx
Using Windows Firewall.
http://www.microsoft.com/windowsxp/using/networking/security/winfirewall.mspx
How to manually open ports in Internet Connection Firewall in Windows XP.
http://support.microsoft.com/kb/308127
How to Configure Windows Firewall on a Single Computer.
http://www.microsoft.com/technet/security/smallbusiness/prodtech/windowsxp/cfgfwall.mspx
Troubleshooting Windows Firewall settings in Windows XP Service Pack 2.
http://support.microsoft.com/default.aspx?kbid=875357
In conjunction with WinXP SP2 Firewall use:
Seconfig XP 1.0
http://seconfig.sytes.net/
(
http://www.softpedia.com/progDownload/Seconfig-XP-Download-39707.html)
Seconfig XP is able configure Windows not to use TCP/IP as transport
protocol for NetBIOS, SMB and RPC, thus leaving TCP/UDP ports 135, 137-139
and 445 (the most exploited Windows networking weak point) closed.)
OR
Configuring NT-services much more secure.
http://www.ntsvcfg.de/ntsvcfg_eng.html
Consider this:
1. Do not work as administrator, use limtited user account (LUA) for
day-to-day work.
2. Keep your system (and all software on it) patched.
3. Review use of IE and OE.
4. Don't expose services to public networks.
Good luck