Vista/Windows 7 Dual Boot - Format Vista Partition

Solution 1:

Since Vista was installed first the boot files will likely be located on C:.

If you want to format C: win 7 won't let you from inside Windows since it will cause boot problems. Easiest way to perform the format is to boot from your Windows 7 media and then start the install. At the harddrive selection screen you can format C: and then cancel the setup.

After you have done this Windows 7 will not boot. To fix the issue you boot from the Windows 7 media again and instead of Install now you select repair at the bottom left corner. At the repair menu you select automatic startup repair and let it finish. This should restore your boot files and give you a working system again.