Format would be the easiest option. You can stuff around and remove the virus, but usually the damage it's caused means you end up running into more problems later...
If you want to go down the trying to remove it path.
1) Backup all of your files, as you may or may not loose everything.
2) Disable system restore - Control Panel - > System -> System restore
3) Reboot into safe mode
4) hit up an online scanning site, such as
http://housecall.trendmicro.com
5) remove anything it finds.
6) Also download an up to date virus scanner and run that
That should remove the worst. I wouldn't be doing anything like online banking until your certain everything has been removed.
Also Antivirus isn't exactly expensive, you can pick up most of the big home based versions like Trend Micro PC Cillin or Mcafee for around $100.. That said theres quite a few free versions like AVG or Avast which are all really good and offer most of the same features as the paid ones.