I'd recommend a few different apps to replace PC Guard (all free).
For Antivirus, I'd recommend Avast (
http://www.avast.org ) Antivirus. A lot of people recommend AVG as well, but I have found Avast to be reliable, and various independant tests say it is thorough.
For Anti Spyware, I'd recommend a combination of programs.
Spybot. This provides good detection of Spyware, and is effective at stopping it being installed.
Spyware Guard . Similar to the above spybot, can prevent installation of spyware.
Windows Defender is a good defence as well. It can protect both by blocking known spyware programs (even to the point of detecting suspicious behaviour by new programs), and scanning. NOTE: If you are using Vista, ,you already have Windows Defender running.