While every enclosure at the office required no drivers, I see you have "XP" and "Windows 2000". These OSes at the service pack noted (none) do not support USB 2.0 so the drive should not work.
Maybe that was an omission by you and you do have a current patched up OS. But then we have the issue that no drive letter should show up. Many will not know to partition and format the drive, and the instructions on the cheap enclosures will not reveal this step.
My new 3.5" External HDD Enclosure USB 2.0 1394a SATA by ST LAb does not work | have tried out in windows 2000 and windows xp platforms
its been detected by the computer initially but unable to install the drivers, so later on i cant access the data drive
if any one can help me in solving my problem