Crap, my current hard drive was cloned with SuperDuper and hence I have the incorrect partition table for Snow Leopard. I'm usually impressed with how smooth it is to deal with Apple, but not so much this time. In practice I can't upgrade to Snow Leopard, but need to reformat my HD and then bring back my backup. Not sure I would've bought Snow Leopard had I known this in advance. - Niklas Morberg from Bookmarklet

Can't you just resize your partition in Disk Utility? Snow Leopard didn't want to install on my Mini that had previously had Linux installed on it and therefore had an extra EXT3 and Linux Swap partition. I deleted the Linux partitions using a Ubuntu Live CD (Disk Utility didn't want to do it). Booted back into Leopard and resized my HFS+ partition to fill the entire drive and then Snow Leopard installed fine. Not sure if my problem had anything to do with the Super Duper one. - Paul Grav

The problem is that my HFS+ partition (the only one I have and it fills the entire disk) has the wrong partition map (Apple partition map instead of GUID) and AFAIK I can't change that without wiping the disk. - Niklas Morberg

Crap indeed! Why would Super Duper default to Apple partition map instead of GUID? - Paul Grav

Uh, I don't think SuperDuper creates partitions. You create the partitions using Disk Utility. Super Duper just does the copying. - Paul Franz

Yeah I'm not sure SuperDuper is the one at fault here. My current drive was cloned via SuperDuper and I upgraded to Snow Leopard fine Friday night. I partitioned it with Disk Utility though. SD doesn't partition. - ronin

Given your comments I probably know what happened. I cloned my internal drive (250G) to an external one (500G) with SuperDuper and the external must've used apple partition map. Then I swapped drives and put the external drive in my Mac and it now has the wrong partition map. (Although everything has been working perfectly until I tried to install Snow Leopard - no warnings or anything.) SuperDuper is probably not to blame, although a warning pop-up in SuperDuper when cloning between drives that have different partition tables would've been prudent. Had I known then what I know now I of course would've made sure that the external drive had a GUID partition table. - Niklas Morberg

SuperDuper defaults to Apple partition map instead of GUID to make drive accessable by PPC systems - Stephan Romeo

Snow Leopard installed and running. On the upside restoring my Time Machine backup after having formatted the disk worked like a charm. Faith in Apple restored. - Niklas Morberg