Use DiskPart to remove GPT partitions

The standard Windows XP GUI tools will not allow you to modify a disk which uses the GUID parition table (GPT) instead of the standard MBR. This is a particular problem if you have used an external disk in a Mac; for example, I used an external HDD as the TimeMachine backup device on a friend's MacBook. Now that she has her own external HDD, I wanted my disk back, but Windows appears not to recognise the disk.

To the rescue comes DiskPart (courtesy of pitumbo).

DISKPART> select disk N
DISKPART> clean

DiskPart itself has a range of useful options for managing and inspecting disks, partitions and volumes. For example: