There is some confusion people have as to the difference between anti-spyware products and registry cleaners. Each scan for different things.
A registry cleaner will look at the windows registry and look for errors. It does NOT scan your entire hard drive looking for suspicious programs. Often, registry problems are not caused by malicious programs. The windows registry can get errors just from the continued use of your computer.
A Spyware Cleaner, on the other hand, looks for suspicious programs, and removes them. It doesn’t generally try to fix errors in your registry. Rather, its purpose is to find and delete malicious programs on your machine.
Since they perform different functions, I would recommend you get both a registry cleaner and a spyware cleaner.