Hello mjk and welcome to the forums
Firstly, have you tried any bootable anti virus CDs? Such as the AVG rescue CD:
AVG UK - AVG Rescue CD
When you boot from this, you will be able to scan for viruses without Windows having to start. This should remove the virus, but I can't promise anything, nor can I promise that this will solve the whole problem.
It is worth a try before you do either of these:
There are a few methods that I can think of to help you, so I will run through them with you:
1. Boot from a Linux Live CD:
Download | Ubuntu
You will need to burn this to a CD, and then boot from this CD. Linux is an operating system and it is renowned for having its'
Live CD function. Basically, you won't be starting Windows at all (and not the virus), but you will be starting Linux and from here, you can copy your documents to an external hard drive and then do a clean install and transfer them back.
2. Removing the hard drive and connecting it to another computer
You will need to buy something along the lines of this to do this method.
IOMAX USB 2.0 to SATA/IDE Adapter Kit with Power: Amazon.co.uk: Electronics & Photo
This cable will allow you to connect your hard drive to another computer and recover the documents. You will need to have the hard drive removed from your computer, and you will then need to connect it to another computer to transfer the documents and then do a clean install.
Please note that by doing this, you may need to get a professional to do it for you because it may void your warranty. You also need to ensure that you scan the hard drive before you copy the contents.
I would personally recommend option 1 because it is much easier (and cheaper), but ultimately, it is up to you?
What are your views on it?
Tom
EDIT: Do you have a Vista Installation Disc?