[azasadny]

Paul,
It's very easy if you have a "USB to hard drive adapter", you don't even have to open up the PC to do it, you simply hook up the "infected" hard drive to the adapter and your PC will see the drive. Use the AV tool of your choice (I use MalWareBytes, Norton Power Eraser and Microsoft Security Essentials) and start the program and select the drive you want to scan and clean, then select the infected drive that you hooked up to the PC and you're all set.

If you don't have the adapter, you have to open the PC and hook up the hard drive as an additional drive and this can be a lot more intimidating, especially if you're not familiar with the innards of a PC. The adapters are very inexpensive and I buy them through Amazon. One of the tools in my PC toolkit...