While attempting to install Ubuntu 7.10 on a USB drive my Windows Vista Boot sector was overwritten by GRUB Loader and the system won't boot. Any suggestions on how I can get Vista working again?

Tried to install Ubuntu 7.10 on a USB drive attached to my laptop using the CD (the laptop has Vista Home Basic installed on the harddrive). After running the install routine and atempting to reboot the laptop either from the USB drive or the internal hard drive a GRUB Loader error is displayed and I cannot use either operating system. Any suggestions on how to restore the boot sector on the internal harddrive so that it runs Vista again? I'll deal with getting the USB drive to work with Ubuntu as a second task.