This was posted on the forum last year and I thought it was worth mentioning here.
This topic has two methods of installing Mac OS in SheepShaver using a restore disk or a system specific install disk (the kind that come with a Macintosh computer). These disks can normally only be used on one machine (e.g. a G4 Cube restore disk can only be used on a G4 Cube, and not on anything else)
Read it here: http://www.emaculation.com/forum/viewtopic.php?t=3119.
— Stephen Coates, October 2, 2007