The registry is the backbone of the Windows OS. Viruses and Spyware change the registry settings to add items to the startup. Most antivirus do not offer protection for the registry. The freeware below is able to provide this protection by notifying the user when the registry is being changed.
RegistryProt is a free software that provides registry monitoring and protection. It monitors important keys in the windows registry and alerts the user when a key is changed or added. It then allows the user to delete the key or revert back to the original settings.
The program is very compact (30kb) and uses very little memory while running. The software does not seem to support Vista. If your antivirus does not offer protection for the registry, you might want to grab this.