Debian Live Multiarch ISO Howto
"Multiple machine boot CDs can be created with the following manual procedure. This procedure has been successfully used to create a single CD which is bootable on alpha, i386, pmax, and sparc. It should be possible to also make the CD bootable on macppc, vax and on sun2, sun3 and sun3x.
To create a CD which is bootable by multiple architectures, use the following steps in this order."