Long shot, but does anyone have any experience with this?
Just need an on/off with speed control.
Any advice welcome.

For hardware interfaces, check these out:
http://www.anyma.ch/research/udmx/
http://www.opendmx.net/index.php/Open_DMX_USB
http://www.opendmx.net/index.php/DMX_USB_Pro
http://www.enttec.com/index.php?main_menu=Products&pn=70304&show=description&name=dmxusbpro
http://www.opendmx.net/index.php/DMXking_USB_DMX512-A
http://www.dmx4all.de/index.html
http://www.skpang.co.uk/catalog/product_info.php?cPath=140_142&products_id=663

Haven't tried any yet, but I'm gearing towards anyma uDMX, because they have Pd examples up on the website.

As for the exact DMX commands you're looking for, I don't have a clue, just getting into the protocol myself. This could be a good intro:
http://www.arduino.cc/playground/Learning/DMX

Nice one Danijel, those are definitely interesting, I guess the uDMX is a little scary though as it draws the power direct from the computer USB?

Anyhow, I wasn't quite clear enough sorry, looking for something sans Pd and computer hence me posting in "Off topic".

I want to be able to control the speed of a motor using the lighting desk FOH. Have been looking at control boards and relays for servos:
So far I've found this but as well as being a bit too pricey, so far as I can tell it is outputting 12V 5A which means any motor I use is likely to be relatively expensive and loud.
So I'd need a secondary relay stage to run something like this?
Arduino is an option, but I'd rather spend as little time programming as possible on this project as I'm already strapped for time.