This drive is plug and play in Windows XP providing your usb port(s) are working so I'd check those first in Device Manager to insure they're working ok.
Does it work properly on a different system?
No error messages of any sort regarding this nonrecognition?
At the very least...I suggest connecting it to known good system and running chkdsk /r on the drive in question.
How to run chkdsk /r from the Recovery Console:
1. Insert XP CD. When the "Welcome to Setup" screen appears, press R to start the Recovery Console.
2. Type the numeral "1" to choose the installation that you need to access from the Recovery Console.
3. When you are prompted to do so, type the administrator password. If there is no administrator password, leave it blank and just press ENTER.
4. At the command prompt, type chkdsk /r, and then press ENTER.
5. When Chkdsk has finished running, read the results, and then take any necessary steps to complete the process.
6. Restart the computer, if it does not restart on its own.