Rule for for dual-boot. Windows gets first dibs.
Anyway, this is for when crap happens with Grub and you want at least Windows back.
1.If XP, boot up with Windows CD. Get to the C:\ prompt. Type "fdisk /mbr" withour quotes.
2.If Vista, boot up with Windows CD. Get to C:\ prompt. Type "bootrec /fixmbr" without quotes.