GUID as the partition mapping... intel Macs have that, the PPC ones before then had open firmware.
GUID as the identifier.. well, there's UID.
If you are in 10.5, man dscl.
If pre-10.5, http://macosx.com/forums/mac-os-x-s...1-osx-numeric-uids-any-control-over-them.html
What are you trying to do with the UID?