For those of you who seem to want more than the single serial port on the empeg, seems I've found a possible solution.
http://www.EDASce.com/serialedas.asp
Seems to allow communication to 2 or 4 (based on model) serial ports through ethernet. They have 'drivers' for unix in the form of C source code.
It's not meant for a car application, but that hasn't seemed to stop some other projects I've seen (Airport wireless). I'm slightly behind on sleep right now so I won't try to say anything actually intelligent on the matter. Just wanted to get it posted before I forgot about it ;)
~Blake