Microsoft purchased Giant Company Software's antispyware program in December of 2004 and now offers that software for free under its own name. I've found the software works very well at detecting and removing adware and spyware. It should be easy to install and use, even for users who aren't particularly technically proficient. The only negative factor I've found with the product is a lack of a capability to generate report files.
The sofware can be downloaded from Microsoft® Windows AntiSpyware (Beta).