Linux-Controlled Legos...

[l008com]

Here is my plan. I wanna load YDL (or MkLinux) onto an old 6100. Then I want to connect that 6100 to a custom built voltage regulator. Then I want to connect THAT to my Lego train tracks. Then I want to run apache and php on this 6100, and great a web control for it. The apache/php stuff is easy, but I'm wondering just how hard the rest would be. Making a voltage regulator that can be adjusted via a Mac Din-9 serial port, connected to a mac running linux. Any thoughts?
Also any ideas on where I might find more hardware hacks like this?