I once had Windows, NetBSD and Slackware installed on the same disk, with LILO as the boot loader.
Nowadays, to keep things simple, I bought a second HDD and configured the BIOS to use the first disk. When I want to boot the second disk, I use the BIOS loader (same principle: default option in N seconds or/plus selection via F11/arrows for other disks). ... The problems with MBRs are now just a distant memory.
PS: Since I recently found out about the "
Return of the Jibbed", I'm thinking about keeping the OSs on external flash drives, but that's work in progress...