You will not be able to format your C: drive (I'm assuming this is your only mapped drive) while windows is running as this is the system partition.

The easiest way to format is to put in the CD and restart the computer, it should then boot off the CD and give you a number of options ... (If it does not, enter the bios - usually press [DEL] during startup - and make sure that the CD rom drive is your first boot device)

You will have an option to 'fix installation' or 'install new'. Install new, and delete the existing partition.

Formatting your C drive will wipe out EVERYTHING on it. It is a big step. You need to make sure you have backed everything up. And if you're not very computer-savvy it could become a long and painful process.

Before resorting to a format, have you tried free anti-virus and anti-malware software to clear the infection? Avast or AVG, and Spybot Search and Destroy. People will tell you that they cannot gaurantee clearing out the virus, but then nothing in life is gauranteed. They will solve the vast majority of common problems very easily and quickly