Try using a disk sanitizer. -or- I am guessing you can hold down the F8 key on startup and start in MS-DOS mode and format your hard drive from there.
Since I have yet to format a Vista machine in this way, I do know that I successfully formatted a drive with Vista on it when I purchased a new PC a couple months ago via installing Ubuntu/Fedora. I didn't even login to Vista for the first time--Ubuntu and Fedora kicked it right off my hard disk platters -hahaha Vista didn't get a chance to live on my PC.
Also try using the Vista install disc if you have it and format/partition from there.