Modifying/ uninstalling GRUB

I got it from another site but don't remember the address anymore.

A) Using a DOS or Windows 9x/ME Boot Floppy

In case you have DOS or Windows 9x/ME on your system, you can use
fdisk for this purpose. Create a rescue disk in DOS or Windows 9x/ME,
use it to boot the computer, and execute fdisk as follows:

fdisk /mbr

The MBR will be rewritten and GRUB will be uninstalled.

B) Using Windows XP

In Windows XP, you can uninstall GRUB as follows:

Boot from the Windows XP CD and press the "R" key during the setup in
order to start the Recovery Console. Select your Windows XP
installation from the list and enter the administrator password. At
the input prompt, enter the command "FIXMBR" and confirm the query
with "y". The MBR will be rewritten and GRUB will be uninstalled.
Press "exit" to reboot the computer.

C) Using Windows 2000

In Windows 2000, you can uninstall GRUB as follows:
Boot from the Windows 2000 CD and press the "R" key during the setup
and then the "K" key in the following menu in order to start the
Recovery Console. Select your Windows 2000 installation from the list
and enter the administrator password. At the input prompt, enter the
command "FIXMBR" and confirm the query with "y". The MBR will be
rewritten and GRUB will be uninstalled. Press "exit" to reboot the
computer.

E) Using Freedos

If none of the above-mentioned boot media is available, a floppy or CD
image from a free DOS system can be downloaded from
http://freedos.org/freedos/files/. You can create the CD image with
any burning program on any operating system. Just make sure not to
create a data CD but a CD image.

Creating the floppy image with Linux:

Enter the following command (or equivalent) in a root shell:

dd if=/tmp/fdos1440.img of=/dev/fd0

Creating the floppy image with Windows:

The directory /dosutils/rawrite/ on the first CD/DVD includes the
program rawrite.exe that can be used to write the image to a floppy.
Copy this program to the directory containing the file fdos1440.img.

Insert a floppy in the drive and start rawrite.exe. Enter the file
fdos1440.img as the source file and confirm with Enter. Then enter the
name of the floppy drive (usually "A") as the write medium. The image
will be written to the floppy.

Boot from this CD/floppy and select "1" for "Boot FreeDOS Setup" first
and then "3 - Clean Boot" from the start menu. Start fdisk with:

fdisk /mbr

By doing this, the boot loader GRUB will be overwritten.