As Husse said in his post:
It's not grub that picks up what you have installed but rather the installer, and the standard varies considerably. The debian based distros I've installed has behaved well - the others not.
I still can only imagine your partition layout, and then guess what may be happening. And I hope to avoid throwing salt in the wound of frustration - been there, done that; read all about it too many times. Not good for either of us.
You can only have 4 primary partitions: hda1 - hda4 or if you have SATA drives they are labeled sda1 - sda4. hda5 (or sda5) and above need to be an extended partition.
Please list how you have partitioned your drive(s):
1) where the root "/" partition is located for the Linux distro's (A, B, C), if you have windows installed what partition it lives on, whether you have a separate /home partition, size of the drive. Sorry I'm a visual learner and I need to get a picture.
2) what Linux distributions are you trying to install on the same machine.
If you are installing two Debian based distro's like Ubuntu and Mint you should not have a problem with grub identifying Ubuntu, Mint, and windows and listing them for selection in the grub window at boot-up.
Where I had my problem the first time was mixing a Mint and PCLinuxOS distribution (PCLOS is a Mandrake derivative). When this happened I had to open my computer and browse to boot/grub/menu.lst make edits to add Mint back into the menu.lst .
Ok I can just hear you saying how. In my case I was really new to Linux, but I had another machine with Mint installed on it, so I copied the menu list from that machine, moved it over to the problem box desktop, opened terminal and typed:
The text editor opened the menu.lst file.
Then I open the menu.lst file on my desktop (just double clicked) copied the Mint menu list commands in grub and pasted them into the menu.lst file that I opened with sudo, saved the file when done closed it and rebooted. When the grub menu presented I had Mint and PCLOS selections. There are other ways to do this, but hey a nOOb does what a nOOb has to do.
Note: the menu list items will be:
title Linux Mint, kernel 2.6.20-16-generic
kernel /boot/vmlinuz-2.6.20-16-generic root=UUID=############ ro quiet splash
title Linux Mint, kernel 2.6.20-16-generic (recovery mode)
kernel /boot/vmlinuz-2.6.20-16-generic root=UUID=########## ro single
where #### depends on your machine.
Someone like Husse or scorp123 could have typed a shorter more appropriate how to. Sorry for the long post.
Btw here's one of the first how to posts that I read when setting up multi boot machines.