Since you are mentioning a ribbon cable that would be an ide drive with a cable seeing three connectors with one going to the main board. Depending on the board most will see the drive's jumper moved to the MA or MS position being master when using the connector at the end of the cable.
For adding in a second drive onto the second middle connector the jumper is set either as SL or SA for slave or left at CS for cable select. The jumper is a small plastic cap that reaches between two rows of small pins recessed into the casing at the rear of the drive itself. Generally there will either a label or stamped set of letters showing where to plug in the jumper cap for each position.
If the drive being added in already has a valid NTFS type partition and is formatted XP or Vista will automatically detect and install it as a new device. It will then appear as another drive letter shifting the D optical to E by default. Drive letters for second hard drives and optical drives can be reassigned afterwards to correct that if needed.