It's a standard 2.5" to 3.5" hard drive adaptor. One end plugs into the 44pin IDE port of a 1200, and a 40pin IDE cable plugs into the other end. Then you can use a 3.5" drive in a 1200. If you add some insulation, the 3.5" drive nests nicely underneath the keyboard ribbon.
Alternatively, Redmond Cable can probably wire up a single cable for you that does all this with less clutter inside the case.
