how to connect a modem to the PS2 port?

[ches]

I am using a laptop as a server, and need a second serial port on it.  I'd
love to use the psm0 port (I know it is an RS232C serial port) connected to
a modem, but I am guessing the the psm driver is getting in the way.
It is hard to ask the right question in Google.

Anyone know how to use the PS2 port as a simple serial port?  I never
use a mouse on this machine.

Bill Cheswick
ches at cheswick.com