Try Avast Free program and also
www.lavasoft.com has a great free program called AdAware that kicks butt.
These virus' almost always put a file in the C:/Windows/System32 folder...
what I do when I suspect a virus, is go there, hit view by modified date and then the last column at the bottom of the page will have the most recently added files there...right click on those and you will see the date that those were added...usually they have an odd name such as "daerfdxx.dll"
you can copy the name and Google it and you usually will get info on whether that is a virus or not..
another thing you can do is Ctrl/Alt/Delete and check the running processes on your system... lots of virus and spamware go by weird names such as "biz.exe" etc. and you can Google those as well..
Run Avast or AdAware software on Startup that way these files can get deleted before they boot up in your OS...
a Final thing you can do which usually works is do a System Restore to a prior date so that all programs installed after that date (including spyware) are rendered Moot...
Go Start/Accessories/Systemtools/SystemRestore for that