Time to go to http://www.ubuntu.com/

Download the CD image and put it on a CD, start the PC up and tell it to run the CD right after being powered on, A lot of the time the computer will do this automatically if a CD is in the drive, or you may have to press F12 or something similar and choose to "boot from CD".

This will enable the PC to at least get on the internet in most cases, and probably do other stuff too. You could even install this to use instead of Windows, and it will not get a virus, ever. It may NOT run a lot of business software though, like quickbooks or the like.