what you need to do is wack the cd in the drive and restart, then it should recognise the CD just after post screen, it will ask you if you want to boot from CD say yes, agree to the license (press f8) then delete the existing partition, and format, then it will wipe everything on your hard drive, be advised tho its best to make sure you at least have a back up of your modem drivers if needed, at least if you have driver probs you can get on the net to find drivers etc.

If it dont boot from CD, you may need to go into the bios and make the CD rom the first bootable drive

I hope this helps