I managed to get the problem resolved. It was quite painstaking, but I'll summarize the other things I did to fix the problem.

- Visited Jotti (http://virusscan.jotti.org/) to find out which AV programs picked up the virus

- Only about 4 AV Progs detected the virus

- I uninstalled BitDefender and downloaded Kaspersky Internet Security after doing the free online scan.

- I ran the program and managed to delete the viruses.

- I ran Registry Mechanic again to get rid of any remnants of the old AVs.

- I ran ScanDisk to make sure all system errors were resolved

Kaspersky deleted the viruses with little fuss, but also picked up some security vulnerabilities. Most of these related to the QuickTime program. I didn't install this! It's a new PC, so it may have been pre-installed.

I just uninstalled QuickTime, rather than doing an update.

If you have QuickTime and don't use it, just uninstall all traces of it from your PC. It seems to be the cause of this virus to some degree. Moreover, it's not an essential program...

The PC is as good as new again and I'm taking active steps to prevent anything like this happening again. It was, in a word, hellish.