You can do it from inside the Windows 7 installer. So you'd boot to the Windows 7 installation DVD and then you will be able to format it from in there. If you want to do it that way, then I can show you how. It's very easy.
By the way, formatting doesn't touch the data: it basically just replaces the Master File Table with a blank one (in the format specified) which is kind of like a Table of Contents. If the Master File Table is blank, then the hard drive appears to have no data on it. For this reason, data recovery is still possible (and easy) after formatting.
Why do you want to do this though? Are you looking to start over to get a fresh start?