Again, thanks for all your help.
M.Mouse, the instructions on your link look as if they'd certainly do the job, but unfortunately, I can't do anything at all on my computer, it seems to be completely disabled. If I try to run the add/delete programs, it won't let me, and an 'infected' message pops up.
The same happens if I try to right-click on the anti-virus icon that has been installed. I can't get on the internet at all, and programs such as Word, etc. will not run, just bringing the pop up message 'infected, buy and run our program to clean' (or words to that effect), up.
I'm going to try the boot in safe mode suggestion tonight, but am not sure whether it'll let me do that or not, I suppose it is determined by how soon after applying power to the computer does the virus activate.
I've encountered a few virus' in the past, but nothing that AVG couldn't get rid of, and certainly nothing as vicious as this one appears to be.