Don't be too quick to blame your friend; this appears to be a common problem with Vista. Unfortunately, there doesn't seem to be a general solution for it.
Have you tried booting with the Vista DVD?
I'm not sure if Vista has Recovery Console, but you can give it a shot (information
here). If you can, open Recovery Console by pressing F10 or R at the Welcome To Setup screen when you boot with the Windows CD. When Recovery Console opens up, try running
chkdsk /r (just type it in and hit Enter). Let us know the outcome.
Do you have another OS disk you can try booting with?