You can have as many chainloader boot entries as you like.
I have had over 20 such boot stanzas at one time ...... difficult to go through the list to find exactly what I wanted
title Linux name
Change the X
to choose the HDD
Change the Z
to choose the partition on that drive.
I used a slightly different approach eventually.
I had only the chainloader entries for each disk in the menu.lst for that disk.
That helped keep the entries down to a manageable number in each.
The only edit you should need to make to the main menu.lst is if you add another partition to the disk.
Be sure you install Grub to the boot sector of each partition that holds an OS.