If the caddy came with a drivers CD...that would have to be installed for it to function properly. If it did not come with drivers, then it should just be plug 'n pray
What is the make/model of this caddy...how do you know it works properly?
What I would do: Remove the hard drive from the enclosure. Attach it directly to my system (temporarily) on the IDE cable currently connected to the CD/DVD drive (remove the CD/DVD power connection). Reboot XP and see if the drive is detected via direct connection to the system. I would change the jumper on the drive to either Master/Slave or Cable Select, whichever I prefer (I use Cable Select for all my drives).
I would first check to see if the BIOS picks up the new drive...then I would check Disk Management...then My Computer.
That should eliminate the drive itself as a possible problem.