Beside my AntiVirus Eset Nod32 AntiVirus v3 Business Edition I don’t use any special anti-spyware tool, but if I do, I prefer Lavasoft Ad-Aware SE. After installing disable that (those?) lavasoft service(s) that, (of course) automatically starts up with Windows, in the Services Manager (Start -> Run -> services.msc). Scanning once a week should be enough. You don’t need full time spyware protection if you also use an antivirus product.