Boot the computer with a Linux live CD. Copy your data over to an external drive. Wipe the original drive with DBAN, which is another live CD. Run two different virus scans against your data on the external drive and weed out any files which pop up as infected. Reload your drive with your OS and keep your data on either a separate partition or preferably another drive. Backup your data at least weekly or more frequently if it is really important.
Time consuming, but not difficult.
Backups - its not a matter of if but when.
Be safe.