I have a 120GB Western Digital Passport external USB hard drive.
It works and is visible in my HP Pavillion dv1000 notebook that runs XP Home.
But, it does not work in my Shuttle SFF box that runs XP Pro. When I plug the cable into the USB port, nothing happens except that the blue light comes on on the WD Passport case, which means that it is receiving power from the USB port.
I went into the Windows Services and checked and started all of the services that I thought would be relevant. Yet, the WD does not show up in Windows Explorer as it does in the HP Pavillion notebook.
The WD Passport does not require special drivers, so says the specs. The original unit came formatted in FAT32 and some WD synchonization software, which I do not use. I converted the file system to NTFS.