Check Disk Management (go Control Panel->System and Maintenance->Administrative Tools->Computer Management->Disk Management) and see if the drive appears with a large amount of unallocated space. If so, right-click the drive and choose to reformat.
Also, make sure you are running SP2 or later for XP Professional in order to avoid the known partition size limitation.
I downloaded CompuApps SwissKnife V3 3.22 after reading the some comments and thought I'll give it a try. I just bought a 1TB LaCie external HD and changed the file system to FAT32, clicked create and and waited until the process was completed. I went to the my computer folder and clicked on my LaCie drive icon and under Details it states the I have a Total Size: 429 GB. What happen to the rest of the 595 GB? Please help!!!!! All I was trying to do is change the system file so that my PS3 can read my external HD.
Windows Version Microsoft Windows XP Professional
Model Intel(R) Pentium(R) M processor 1.86GHz
Speed 1.86 Ghz
Cache Size 2048 Kb