Three Linux Operating Systems in One Computer (Is it possible?)

[Henk Koster]

The various Linux OS-es can all share the same swap partition. Your only
problem may be that each of the Linux installations may install its own
version of GRUB in the MBR of the HD, thereby overwriting the previous
ones. So, you may have to manually edit /boot/grub/menu/lst for the last
Linux version installed to add stanzas for the other Linux OS-es (and for
Windows, if you have that), to get them in the preferred order, and to
indicate the one to start as default. No need to reinstall GRUB in that
case. 

This works fine for me running: 1. Ubuntu Dapper 64-bit (default,
installed last); 2. Ubuntu Dapper 32-bit (installed first); 3. Gentoo
64-bit (installed last, skipped emerging GRUB).