What I mean is booting multiple OSes from the same family off of one CD. When you get an MSDN subscription, Microsoft sends you OS CDs labeled as "versions". There is a Windows 2000 Versions CD (with Professional, Server and Advanced Server all on one CD), a Windows XP Versions CD (with Professional and Home on one CD), and a set of Windows Server 2003 CDs with 2 versions on each CD. When you boot from the XP and Server 2003 CDs, you get a menu asking which version you would like to boot. The Windows 2000 CD, unfortunately, doesn't have this boot menu.
In our test lab at work, I try to keep the latest OS CDs laying around. I slipstream the latest service pack in to the OS, and create an unattended installation to make setting up a system much easier. Rather than keep a CD for each individual OS, I would rather slipstream the versions CDs and be offered a boot menu to choose which OS to install. I can slipstream the XP and 2003 CDs and leave the boot menu intact, but I need to create a boot menu for the 2000 CD. I would also like to create a bootable DVD with all four of the Windows 2003 versions on it.
Hopefully that verbose response helps answer your question! A boot menu may work for different OSes on one CD, but I'm really looking for a menu to help with booting similar OSes that are created with symbolic links to optimize the file system.