Sometime back I had a virus issue, despite being religious about running anti-virussoftware, not opening strange attachments, not going to weird sites, etc. When I finally got it fixed (after having to re-format the hard drive, reinstall Windows and recreate almost everything) I ditched McAfee and Internet Explorer and switched to MS Security Essentials and Mozilla Firefox. Have had no problems ever since and everything seems to run much more smoothly.
Oh yeah. Also run Spybot frequently.
I also switched from McAfee to MS Security Essentials. Tried to install Firefox, but it crashed - I think it's another Win 7 x64 issue. Will add Spybot to my tools.
Many thanks to you and everyone else who has responded.