Not sure about Windows 7, but on Vista it can apparently be sorted using the Windows disc if you have it
To repair your BOOTMBR:
- Put the Windows Vista or Windows 7 installation disc in the disc drive, and then start the computer.
- Press a key when you are prompted.
- Select a language, a time, a currency, a keyboard or an input method, and then click Next.
- Click Repair your computer.
- Click the operating system that you want to repair, and then click Next.
- In the System Recovery Options dialog box, click Command Prompt.
- Type “Bootrec.exe /FixMbr”, and then press ENTER.
I’ve done this several times after having problems with Grub and linux installation.