Hi!

You can make a partition on your hard disk and install another linux distribution, this new distribution will install grub in the MBR sector, i.e. it will overwrite the original grub installation.

(Better for this example, if you install a linux distribution capable of recognize another linux version already installed and add it to the new grub menu.lst (I know that Ubuntu can do that...). Recently, I installed FEDORA in a computer than already has UBUNTU, and then I had to do a lot of things in order to see my UBUNTU partition again in the Grub menu).

Returning to your question, now you can login in your original partition and format the partition where you have installed the new linux (you can use a disk partition tool, like parted), so when your computer restart, grub will show you and error message. (I guess...)

Now you have to fix your MBR....

Another form... is making a new partition and install windows :-( .... that will overwrite the MBR and you will not see your grub again... so you have to fix your MBR...

If you have already installed windows in one partition (dual boot with linux) you can execute in the console fdisk /mbr or fixmbr (winXP), I don't know the command in Windows Vista. This command will overwrite the MBR sector... i.e. it will erase grub... and you have to fix your MBR....

The last way that I can imagine is having a dual boot windows/linux use partition magic or similar to format the linux partition... when you restart the machine, you will see the grub error message... so you have to use a rescue disk to enter to windows and fix the mbr....

Good luck!

Maria C. Bessega