Yep, I'll do this by default now. One "Master" bootloader in the MBR that points to the different partitions holding the bootloaders of their OS.
Only 2 things are neccessary:
Added at 2011-10-18:
grub configuration entry (from the MBR bootloader configuration) to boot the next boot loader (from a partition):
title Partition 11 RedHat 5.2
This causes the bootloader from the 1st disk / 11th partition (numbering starts with 0) to be executed.
For additional notes for grub and multi-OS installations have a look at http://www.dedoimedo.com/computers/grub.html for instance - but there are many grub tutorials out there...
One additional note regarding RedHat on high partition numbers:
Default Linux is able to work with up to 255 partitions on an IDE disk, but RedHat crippled fdisk with a patch to only support 8 or 16 partitions (don't remember exactly). I worked around this problem by installing RedHat Releases on low partition numbers, and moved them to higher partitons after the installation. I recommend therefore to use another distribution (I used a small Debian installation) as a base OS to administer the other installed systems (moving them around, perform backups and such).
And yet one additional note regarding Linux & swap files:
If not mixing old Linux systems with current distributions, all installed Linux systems may use the same swap partition. Otherwise you may have to set up 2 partitions as swap partitions, since the format changed once in the past (I don't remember when exactly - just keep one spare partition as fallback if you intend to install historic Linux distributions later and experience problems with the swap partition format)