Hi James_43 - Check out these tips for removing viruses from Windows Vista - http://windows.microsoft.com/en-US/windows-vista/How-do-I-remove-a-computer-virus
If you have the original Vista installation disk, you can reinstall Vista, but it is always best to try to remove the virus(es) first. To reinstall, just pop in the Vista disk and follow the instructions given.
Hope this helps!
Microsoft Windows Outreach