1.Download and Install SP2 if it's XP, SP4 for 2k from microsoft.com
2.Download, Update and run Avast antivirus from avast.com;
3.Download, Update and run Adaware (lavasoft.com) in safe mode with networking.
4.Online scan @ http://www.bitdefender.com/scan/licence.php or http://support.f-secure.com/enu/home/ols.shtml
It's should take care of 99.99% of the spyware problems.