Your PC is infected so that part? You need a clean virus, spyware, malware, ... radical? You must retrieve data from your PC that most?

Then you need a Live CD with antivirus scanning.
The LiveCD is simply a version of Linux that starts directly from CD, therefore without installation. Just download the ISO image and burn a CD and then restart the computer with the CD and you're done.

The following two links LiveCD with scan:
AVIRA - http://www.free-av.com/it/tools/12/avira_antivir_rescue_system.html
Bitdefender - http://download.bitdefender.com/rescue_cd/