OK here is the plan, roughly.
Take a 6100. Load linux on it (probably MkLinux, maybe YellowDog)
To this Mac's serial port, build a voltage regulator that can be controlled via the command line, and set the output voltage of the power-supply anywhere from say... 2 volts, up to say, 14 volts (14 is about what the transformer gives out, so max would just be straight power, no resistance. I don't know nearly enough about electronics to pull this off. But I'm very determined.
The end goal is, of course, to run apache and php on this machine as well, and build a web page that lets me fully control the speed and direction (or at least the speed) of my Lego trains.
:ebc:
The web stuff is easy, what I really need lots and lots of help with is making the actual voltage regulator, and making it with a serial interface. The idea is to make this page local, but if it works I might just put it on my site so people can randomly, throughout the day, turn my trains on and off 
. . . I just posted it in the Duo section of the new HackLinks project:
http://www.artm-friends.at/rm/train/
jt
jt's link is a good one. This may also help.
http://www.oopic.com/oopicr.htm - you may need to split your transformer voltage output to feed it...
--DDTM
That looks good, but where do you get one?
Click the 'Ordering' link off of the home page http://www.oopic.com/
--DDTM