I never tryed to get the arduino reading DMX singals, beacuse sending is allready at the edge of my knowligh, but maybe i can give you some links and help:
reading dmx is quit hard stuff, because of the timing (and the missing clock singal). A DMX bit is 4 Microseconds long, so reading with digitalread(); is no solutiom. I'don't know if this is possible withIn the arduino environment.
I would start checking out if some one got the arduino to read MIDI, this could be a good starting point.
On the other hand there are dmx Resceive using Atmega chips:
there is a dmx receiver, maybe you can ask massiom if he could post the code here, to get a clue how this works
futhermore there is webside german guy called hendrik Hölscher (http://www.hoelscher-hi.de/hendrik/english/dimmer.htm#transceiver
) maybe you can ask him as well for code example
if you just want to get it work fast, build your own transceiver like explaint on hendriks web side and read this dmxtraniseiver outputs with the analogIn pins at the arudino, this is a creapy but fast way
all the bes