Note: This is post as of now only covers grub legacy that is ubuntu 9.04 and previous. The newer versions have grub2 in which some of the steps listed will not work.
If you want have installed windows and linux in a dual boot system , and you make use of the grub to choose which one to boot into. Uninstalling Linux will be little work. Follow the following steps to uninstall Linux and remove the grub.
NOTE: Start this procedure only if you have a windows bootable installation CD
1. Boot into your system and go to the windows disk management ( right click on my computer -> manage-> disk management)
2. Format the partition that has Linux in it. (just right click on the partition and select format. Say yes if it asks you for confirmation).
3. If you reboot the system now, you will be stuck in a screen that might look like this
4. In case you do not have a windows installation CD and want to get into windows from the grub menu, run the following commands
ii. chainloader +1
iii. make active
NOTE: The parameters (hd0,0) to the first command might be different in your system depending on how the windows has been installed. To find out other partition you can use the command "find /boot/grub/stage1"
5. If you have a windows installation cd boot from the cd and go into recovery mode and run the command "fixmbr" and "fixboot"
if you are using windows 7 then the commands would be bootrec /fixmbr
and bootrec /fixboot
6. If they are no errors, then reboot the system using the command "reboot".
If every thing has gone fine you should not see the grub menu any more and boot straight into windows.