From AVG Technologies:
AVG Rescue CD repairs system crashes and returns your systems to operating at full capacity. If malware gets past your security software, you can quickly get your PC back up and running smoothly. AVG resellers have been using this same solution to recover their customers' infected systems and now it's available to your business, free of charge. It's a clean bill of health for your system -- without the bill.
The AVG Rescue CD is provided in two versions: an ISO image that can be easily burned to an optical disk (CD), or a compressed version that can be installed to a bootable flash drive (USB). Once this is done, you can simply boot from the drive of choice directly to the AVG menu, where you can scan for viruses, edit files, test your drive, or even edit the registry. You can also access a number of common Linux tools to make changes to your system.