Model: MDP 3900V-U
Operating System: Windows 2000 (Note: might work with other versions of this os.)
I finally found it when searching Dell's message boards. A tech support person mentioned the this link
in response to a request
The modem drivers required for...
-MDP 3900 PCI Modem Emulator
-MDP 3900V-U Modem
for Windows 2000 Professional