> > Use a magjack with POE support, and leave thru-holes or some sort
> > of connector/header to add-in a Silvertel POE module.
>
>  i like that idea.  do you have any circuits kicking around?

This might be a good example:

http://arduino.cc/en/Main/ArduinoBoardEthernet

Also see http://www.silvertel.com/poe_magnetics.htm

Basically, a POE magjack has 4 extra taps that get
wired to the 4 inputs of a Silvertel 9205 module,
and you get 5v out the other end.

Full datasheets are at:
http://www.silvertel.com/poe_products.htm

http://www.smsc.com/Downloads/SMSC/Downloads_Public/Application_Notes/an1718.pdf

The short version: Make sure the Magjack has transient voltage
suppression built-in, or that you have some zener diodes on
the ethernet phy in case a POE-powered device gets hot-plugged.