the OS installer usually does the formatting these days. unless you need to make sure the old data is not recoverable, there's no real need to format the drive separately.

to start the OS install process you need to boot from the install medium (in your case: the CD, but a prepared USB drive would work on most modern computers and is usually the medium of choice these days). that means, you insert the CD, power down and turn on your PC. then you want to have it start from the CD, not the HD. how exactly you do that depends on your settings, motherboard and BIOS. if your PC is already set up for that, it's as easy as putting in the CD and restarting. maybe there's a select menu asking where to boot from or whether to skip booting from the CD. or booting from a CD isn't even turned on, then you'd need to go into your BIOS and change the boot priority to have your CD drive (or USB) come first.

>>49791
if you are installing windows, the installer has an 'advanced options' button under 'install windows' and 'upgrade windows'. from there it shows all the partitions on the hardrive and gives you format and erase buttons.