See this page from WD's website for technical details:
http://www.wdc.com/en/products/legacy/Legacy.asp?Model=AC2120
You may not be familiar with the way old HDD units like this were set up in BIOS. Today almost all IDE drives are configured automatically by the BIOS, and they do this by reading certain required info from the HDD unit itself. But the old way was that the BIOS MIGHT be able to read that from the drive, OR you might have to enter the settings manually. To do this you go the the BIOS Setup page where the HDD's are configured and detected. For this particular unit you would set the HDD type to NOT be "Auto", and set its type number to 47 (I think). Then you have to enter the specs on that WD page for Cylinders, Heads, Sectors or Tracks, an possible for Landing Zone and Compensation. This unit does NOT have LBA Support.
Note that the WD page also shows you three diagrams for how to set the unit's jumper for "Single" (Master with no Slave present), "Dual (Master)" (Master with Slave present) and "Dual (Slave)". You need to set this BEFORE installing it according to how you connect it to the IDE port and cable. If this is the only unit on that IDE port, set it to "Single" and connect it to the END of the ribbon cable. If this is the Master device on a port that also has a Slave, set this unit to "Dual(Master)" and connect it to the end. If this is the Slave device on an IDE port that already has a Master device, set this one to "Dual(Slave)" and connect to the ribbon cable's MIDDLE connector.
If you get the drive parameters set right in BIOS Setup it should report to you some form of the drive's name and model number, and the correct capacity of about 125 MB. Then you can hope that Windows will be able to read its data and show you the drive in My Computer.