In Windows XP Professional, you can remove the GPT disk by using the clean command in DiskPart, which will remove all data and partition structures from the disk. aka, making it uninitialized.
1. You will see the GPT Protective Partition in Disk Management.
2. Go to DOS command line (click on "Start Menu", then "Run", type in "cmd" in Open:, then hit "OK")
* Type in "DiskPart" in command line.
* Type in "list disk" in command line to show all disks in this machine.
* Use "select" command to set the focus to the specified partition, for eg, "select disk 1".
* Use "clean" command to remove GPT disk from the disk by zeroing sectors., for eg, "clean"
3. Go back to Disk Management, you can see the disk is currently “unallocated”. Right click on disk info, choose "Initialize Disk".
4. In Disk Management, choose the drive and do the neccessary.
p.s. This is done on assumption that, you don't have any 'data' inside, that's still needed.