FWIW, I've just finished characterizing the input voltage range and
power consumption of the Linksys WAP54G V.2 access point, and posted a
graph at
http://compusmiths.com/WAP54G_Power.htm
Basically it'll run on anything from 5V to well over 18V(*), and draws
a maximum of a bit under 3.25 watts. I'd plan on getting 6V or more
to it if I were running it over a long power cable, but it'll actully
run as low as 4.2 volts.
(*) My power supply only goes up to 18.86 volts, and it wasn't worth
trying to exceed that. The limit is probably the input capacitor
voltage rating, which in this instance is 25V, though I wouldn't
depend on that always being true. The supplies Wall Wart (TM) is
rated at 12V, 500mA, but it's unregulated and puts out 17.3V
open-circuit. Since our local guru Jeff L. has measured WRT54G
routers running a bit lower than 4.2 volts, there's probably some
margin for error and/or variation between units, temperature effects,
etc, so I'd supply them a minimum of 5V.
As an aside, there's plenty of opportunity for Linksys to make a
"compact" version of the WAP54G, as the circuit board hiding inside
this standard Large Linksys Box is only 3.1"x5.8"x0.75" (plus
antennas). Looks like it'd be pretty trivial to add a ground wire and
a supply diode between the Ethernet connector and the power connector
and feed it power thru the spare pairs. Then the only 'hard' part of
the power-over-cat5-cable thing is injecting it at the other end of
the cable.