Microsoft Antispyware & Security Essentials
If your not using an antispyware product then try the MS one.
Why? Well its free, it works pretty well, it's better than not having any at all
Visit the Security Essentials site to check you have the latest updates and information in order to protect your systems from spyware, viruses and other exploits
http://www.microsoft.com/athome/security/protect/windowsxp/Default.mspx