I need to support both MacOSX 10.4 (Tiger) and 10.5 (Leopard) for the latest release of PerfectTablePlan. I could have created a new partition on the current harddisk for 10.5, but apparently you can’t do that without erasing the whole disk. I really didn’t want to mess with my existing 10.4 setup, so I purchased a 320GB WD MyBook USB/Firewire external harddisk to install 10.5 on to. 320GB for £75, bargain! But I had quite a bit of trouble installing Leopard on to it. After about the tenth time looking at a “Mac OS X could not be installed on your computer. The installer cannot prepare the volume for installation.” message I finally got it working. In case anyone else gets stuck, here are some hints:

• When you set up the new harddisk partitions using Disk Utility make sure you choose Apple Partition Map using the Options button (it may be set to Master Boot Record if the disk is shipped set-up for Windows).
• Disconnect the harddisk USB cable. Just use the Firewire cable.

I hope this saves someone else a few hours. Thanks to Jeff B for a hint that got me moving in the right direction.