Get serial mouse and Track Point to coex

I have a Compaq Armada 3500 runnint Windows NT Workstation 4.0. The Armada has a Track Point. When I’m at work, I want to use an external keyboard and mouse. The keyboard goes in the PS/2 DIN plug – the PS/2 mouse I want to use goes into a serial port using a DIN/Serial adaptor.

I can’t get the mouse to work, and I can’t seem to disable the Track Point using the Compaq BIOS – any ideas for getting the mouse to work?