One usually needs the windows disc to reformat. At least I've used one the last 5 million times I've reformatted a boot drive. I'm not sure how you intend to make a bootable CD, unless you saved an iso of the disc on your computer, in which case you'd need to have saved the serial also. Maybe someone else knows another way.
Let's see. Once you've got a disc, log into your bios and make sure your boot order is CD, Hard Drive. Then put your CD in the drive and restart again. hit any key when it asks if you want to boot from the disc.
Just go through the prompts and stuff, and when you get to the screen which asks you which partition you want to install windows on, You can choose to create or format a partition. Sometimes you might need to delete a partition and create a new one. Format in NTFS.
That's just the general from memory, but I hope it helps.