Now, Bootcamp is supposed to make this easy – you just launch the Bootcamp assistant, and click “Restore the startup disk to a single volume”. A few moments later, all seemed well, and I was prompted to reboot.

After the reboot, the Windows XP drive is still visible, and it seems nothing has happened. After trying this multiple times and getting quickly fed up, I ruled out a few other ways to delete Windows:

• I couldn’t run the Windows XP installer disk – rebooting the iMac with the disk in the drive caused a “Press any key to boot from CD…” prompt. Unfortunately, the iMac keyboard doesn’t work at that point.
• Attempting to run the XP installer from within Vista – the “Install Windows XP” option is greyed out and not selectable
• OS X’s disk utility wouldn’t let me unmount or erase the Windows parition
• I was too scared to use fdisk from the command line, just in case I nuked my OS X partition (and didn’t want to reformat the whole lot for the same reason)

So, how did I fix it in the end?

If you can’t delete Windows from your Mac’s bootcamp installation:

• Drag the Windows parition to the Trash to unmount it
• Run the Bootcamp assistant and choose “Restore the startup disk to a single volume”

Guess that’s the risk you take when you use Beta software eh?