So far I'm using the Arduino Uno, two EasyDriver boards, and two of the cheap rails with an LED on top to test the concept.

So far has been good. Getting the two motors to spin simultaneously was very easy using the AccelStepper library and following two guides:

• http://www.schmalzhaus.com/EasyDriver/Examples/EasyDriverExamples.html
  
• http://www.airspayce.com/mikem/arduino/AccelStepper/MultiStepper_8pde-example.html
  

As pictures show the results of the actual photos aren't that good. Two main reasons for this I think:

• Light pollution. In both of the photos it was pitch black when I took the photo. Even after adding a pot the LED is still way to bright and is throwing light in all directions. I'll buy some nail polish and paint the bottom/sides of the LED to see if that helps.
  
• The LED itself might be too big. The rails only have less than 6cm travel which means the LED takes up too much of that space... I need a smaller LED.

Next steps:

• Fix light pollution, get a smaller LED. 
  
• Build proper coord system and way to turn LED on/off. At the moment the rails are just moving backwards and forwards randomly.
  
• Build some spacers so rails have more travel. At the moment the rails run into each other and that massive pcb with the LED decreases travel for that rail too.