I'm one of the dial-up diehards - and doing something that sounds very close to
what you're trying to do.

My serial modem is connected to an old computer running "Smoothwall Express", an
Open-Source firewall package.

http://www.smoothwall.org/

My Smoothwall PC runs "headless" - no keyboard or monitor. I get to it via a
web browser running from any other computer on my LAN. Dial-up support in
Smoothwall is a bit quirky, but it does work. I'm very happy with it, and I get
a much better network topology than I had before. Doesn't take much to run it:
I'm using a late-20th century 566Mhz Celeron with 256MB RAM and a 4GB HDD.

If I were still the geek I used to be, I'd combine that software with my file
server, and set up that box as a print server, too...

Might this be the solution you're looking for?