What are the technical and license restrictions around virtualization for Leopard, Snow Leopard and Lion?
Legally, you can only run OS X Server in a virtual machine for 10.5 and 10.6. With Lion, they allowed regular OS X installations to run in up to two virtual machines. VMWare Fusion does support Leopard and Snow Leopard Server virtual machines (but not yet Lion), but I don't know if it will let you use the same installation both booted from disk and in a virtual machine.