Well...if it's not partitioned, then XP would not be able to see it in My Computer.
It would show up in Disk Management...but not in My Computer/Explorer. XP only sees partitions/drives which are formatted in recognizeable formats (FAT or NTFS).
Sooo...you may want to check a few other things out.
The fact that you received a message indicating that a file system is detected...lends credence to my speculation that it is indeed formatted.
I'd take a look in Disk Management for details...Start/Run...type diskmgmt.msc and hit Enter. Details should be revealed in lower portion of screen.
If you so desire, you can also format from Disk Management.
AFAIK, most (if not all) external drives come already formatted...so that owners can use them instanteously. From what I see, a damaged hard drive may display as a RAW file system in XP. It probably would not hurt to run a hard drive manufacturer's diagnostic on that drive.
Hard Drive Installation and Diagnostic Tools - http://www.bleepingcomputer.com/forums/t/28744/hard-drive-installation-and-diagnostic-tools/