Dear All, I have uploaded a video on YouTube showing some LEGO trains equipped with RCX PBricks running on one larger stretch of track: Control is via IR messaging from a PC program talking/listening to the LEGO IR tower traffic. A simple ID/databyte message exchange protocol adresses individual trains on the track (or all). The track is powered with 9 ... 18V DC, as one sees fit. The PBricks are all RCX1.0, pick up power from the tracks via modified 9V trains motors and deliver power back to the motors. The RailBrick Journal Issue 3 (Page 44 and up) has some more information. The program running on the RCX and some other details are also available on the RailBricks website (see building instruction section, Diesels, GP40_RCX). It's up to you what the trains do, just program that into the RCX. I am simple minded, so power level setting 0 ... +/-7 (compatible with the 9V speed regulator, I love compatibility), some power level ramping (internally on the RCX, which allows 25 power level settings for each direction, looks more realistic when going from 0 to 5), head light on/off, some sound generation, and PID speed control (that IS fun!) is what I came up with. I am working on getting the NXT PBrick to be of any value here ... Rock on, Thorsten