I don't know how I managed to do it, but I'm running Leopard on my MBP on an Apple Partition Map.
Anyhow, I got my Snow Leopard disk yesterday and it wants me to reformat to GUID and warns me that it will erase everything. Now I have to figure out how a way to backup everything, install SL on GUID and restore everything while retaining my settings, serial numbers and all that good stuff. Is this possible?