isdn woes

After waiting 3 weeks for qworst to send out an isdn modem,
I am looking at it and it has to be connected using a modem
cable to the com port. I'm an idiot, I thought it would
have an rj45 like a cable modem.

In short, here is what I want to do:

PC's -> Switch -> OpenBSD FW (w/nat) -> ISDN Modem -> Inet

Nearest I can figure, I have two options:

A. Learn how to configure PPP on Open BSD
B. Find an ISDN modem which functions like a cable modem.

Can anyone offer any help?

v/r
Mike