XTrkCAD is a CAD program for designing model railroad layouts. 
You can design layouts in any scale and gauge. XTrkCAD has
predefined libraries for many popular brands of track.  You can
test your design by running trains, and you can print the 
design in a scale of your choice.  When printed in 1:1 scale 
the printout can be used as a template for track laying.

Beginner's Tutorial: http://www.xtrkcad.org/Wikka/BeginnerTutorial
User Guide:          http://www.xtrkcad.org/Wikka/UserGuide