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:
Matthew Skelton 
Hi to all the MacForums folks! Hope you find the details above useful.
M
Partitioning a disk is easier with these tips.