I thought you may be interested in this. George from Chameleon Technology is moving into DMX lighting desks. He has also developed a very powerfull software package for controlling DMX fixtures. The software is downloadable and TOTALLY FREE. You can run this from your PC on its own to control almost anything that is "DMX-able".
If you decide at a later date to add off PC control, you can buy a hardware interface to provide suitable "knobs & sliders", however this isnt essential if you want to do things on the cheap. The software will provide an easy and affordable introduction to DMX control.
Chamsys
Software