If you format the 10.04 partition, this might erase GRUB stage 2, but it's a cinch to reinstall. If you don't like to get your hands dirty on the command-line, just boot the 12.04 CD and install the "boot repair" program (https://help.ubuntu.com/community/Boot-Repair).
The first button in the program, "Recommended Repair" should work to install GRUB again. Or you can go into the advanced options and choose a new place for GRUB.
I have Ubuntu-10.04 installed on sda1..I installed grub 2 to mbr
As 10.04 is near eol I installed Ubuntu-12.04 to sda3 during install it did not offer to install grub 2
After the install I sudo update-grub which addded it to the menu and I can boot it from the 10.04 grub menu
I will be wanting to delete 10.04 upon completion of configuring 12.04
What do I have to do to 12.04 so that I have a working grub 2 menu
At the moment I have 4 distro's all working from grub