So I got my copy of Leopard in my grubby little hands and eagerly stuck it in my MacBook to do an update over lunchtime. It gets to the "select a destination" screen and my drive has a big red exclamation mark in it. Apparently it can't install onto this volume as it needs repartitioning as a "GUID Partition Table" type, and that will of course obliterate the contents. It's currently "Apple Partition Map", which Disk Utility claims will only boot PowerPC machines. Hmmm, seems to have been working like that quite happily in Tiger for a year Ah well, I guess I'll have to wait until I get home this evening, install it on my Mac Pro and then backup the MacBook and do a clean install.