Here is how to restore your GRUB MBR after installing Windows 7 (or any version for that matter).

  1. Grab a boot CD of Ubuntu and boot it up
  2. Open the terminal
  3. > sudo grub
  4. If you have a none standard installation (multiple installations of linux or weird partition setup) then use:
    > find /boot/grub/stage1 to discover where your root should be
  5. > root (hd0,0)
  6. > setup (hd0)
  7. > quit

reboot :)

I personally have 2 different flavours of linux installed and my root happened to be 0,4 and 1,4 as I have 2 drives and each install was on a different partition of each drive. I would recommend choosing the one that you boot into most frequently – as when you install new Kernels etc via apt it will auto configure GRUB for you.