Max Pierson designed a very excellent Arduino DMX-512 I/O shield. 

Please refer to his site: http://blog.wingedvictorydesign.com/2009/04/29/arduino-dmx-512-io-shield/ for more information.

We support his project by supplying bare Arduino DMX-512 shield.

Parts can be ordered at: http://www.cutedigi.com/product_info.php?cPath=284&products_id=4331

 The latest software can be found at:

http://blog.wingedvictorydesign.com/2009/07/10/rev13-of-the-arduino-dmx-reception-software-released/

 An assembled board can be found on his website:

The parts you need can be found on his website too.