By far the best solution will be to reinstall the operating system from the rescue disc that came with your computer, or the original Windows disc.

If you want to save files, you may be able to boot into safe mode, or access files from the other drive?

If you reinstall, make sure the first thing you do is to visit Microsoft Update and download all the critical updates. If you need to reboot, return again to check there are no more.

A operating system which is not patched allows easy infection by malware.

You may want to read this document:

So how did I get infected in the first place?

http://www.castlecops.com/postlite7736-.html

In addition to the advice there, please be careful with email attachments. Many ISP check emails for viruses, but they can still get through. Never claick on email attachments unless you know the person who sent it and what it is- email addresses can be faked.

With any luck we can help you avoid getting in the same situation again!