Returnil is a “powerful virtualization technology that completely mirrors your actual computer setup and it can create a virtual storage disk within your PC where you can save documents, data, and files while using the System Protection feature.”
“ Returnil virtualization technology clones a computer’s System Partition and boots the PC into this system rather than native Windows, allowing you run your applications in a completely isolated environment. Hence the session and all activity, malicious or otherwise, will happen in the virtual environment, not in the real PC environment. If the PC is attacked or gets infected, all you need to do is to simply reboot the PC to erase all changes. After reboot, the system will be restored to its original state, as if nothing ever happened. All of this without sacrificing computer performance or usability while helping to reduce technical support intervention and the need for routine maintenance.”
Returnil is free for personal use on your own computer (business users must pay).
Chris Pirillo has Virtual Machine Speed Tips.