1) Boot with your Vista/Windows 7 installation disk. Hit <Enter> at the language selection prompt then hit <R> for Repair to get to the Repair section.
2) Select the command prompt (console) and type in the following commands:
BootRec.exe /fixmbr (#updates MBR master boot record...do not run if you still want grub)
chkdsk /r
BootRec.exe /FixBoot (#updates PBR partition boot)
BootRec.exe /ScanOs
BootRec.exe /RebuildBcd