Here is how to restore your GRUB MBR after installing Windows 7 (or any version for that matter).
- Grab a boot CD of Ubuntu and boot it up
- Open the terminal
- > sudo grub
- 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
- > root (hd0,0)
- > setup (hd0)
- > quit
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.