"buy a mac" is the response that is getting REALLY REALLY boring.
Glen; what kind of PC is this? Does the PC match the specifications from the vendor? Many anti-spyware apps need as much as 120Mb to run. You could consider turning off some of the realtime scanning features and resorting to a once-a-day scan of your PC instead.
Alternatively, try some of the other scanning apps, my personal pick would be Windows Defender; a free application from Microsoft that gets the job done.