Apple’s new Boot Camp Assistant pulls a neat trick: if you have a single Mac OS X partition on your startup drive – it allows you to non-destructively repartition it and add a partition to install Windows XP.
But what if you’ve already partitioned your drive? Boot Camp Assistant refuses to run and tells you you must have a single partition. Do you really need to reformat to play with Apple’s new toy?
I’ve since installed XP on a MacBook Pro that had already been set up with three partitions without having to repartition. Here’s how I did it:
1) Started up the MacBook Pro in Target Disk Mode.
2) Connected it via FireWire to an Intel iMac.
3) Used Disk Utility (on the Intel iMac) to reformat one of the unused partitions as FAT32
4) Unmounted the MacBook Pro and shut it down
5) Booted the MacBook Pro and held down the option key, and inserted the XP install CD.
6) The XP install CD showed up in the boot picker; I selected it and booted from it.
7) Installed XP as normal.
I imagine that steps 1 and 2 could be replaced with booting from the OS X install CD – the key is that you can’t reformat a partition to a different disk format on the startup disk when you are booted from it, since the entire disk must be unmounted. I haven’t tested this theory (yet).