Your problem is a little confusing, so I'll throw in some ideas and you can pick what ever applies.
You cannot format the active partition Windows is currently running on. It's like picking yourself up with your bootstraps... it won't happen. You can insert the Windows Installation CD, or any number of partition manager boot disks (Hiren's is my favorite http://www.hirensbootcd.org/download/ ), and format the drive outside of Windows.
Edit: Most of the partition managers on Hiren's can be used inside Windows if the built-in partition manager is causing the problem. /edit
If you're having trouble booting into something other than Windows, letting us know what kind machine you're using will help in determining exactly what keys to push (model, part numbers, manufacturers, etc). When you reboot, there should be an option to "press xx to select boot device/order" where you can select your CD drive. If there isn't an option for that, open the BIOS and manually set your CD drive to boot before the hard drive.