OK!  I received the drive caddy.  The blank drive caddy had p/n 4P124.  I am not sure if that is a Dell p/n but the part arrived from http://www.parts-people.com.  I went out and got a 120GB 5400RPM 2.5inch laptop internal IDE drive.

Now, I built my bootable USB stick to install an OS on the new drive which has detected beautifully and dual-boot this puppy.  For instructions to do this, see:

http://owsug.ca/blogs/brad/archive/2008/10/01/Making-a-USB-stick-bootable-for-Vista-or-Server-2008.aspx

Success!

Incidentally, in the boot sequence and as detected devices, Modular Bay drive shows up.  I have no idea what Dell was thinking that this part did not exist...  I installed my second OS and now have a dual boot configuration 1 OS on each drive.

Experiment complete.  I now gained way more functionality from my laptop with a second internal drive!

Read the complete post at http://owsug.ca/blogs/brad/archive/2008/10/01/Mad-Scientist-fever_2C00_-time-to-experiment-with-upgrading-my-Dell-Latitude-part-2.aspx