Have a pair of ATI Radeon X1900 series cards and want to put them to good use when you're not gaming? FAHInfo.org has the g2 on maximizing your WU processing...
"Now you need to get the GPU ID in order to tell the GPU client which GPU to send the cores to. The GPUs are numbered starting from zero so the GPU ID number is always one less than the screen number. In the example above, where monitor 1 is attached to the primary output of card 1: GPUID=0, and monitor 2 is connected to the primary output of card 2: GPUID=1. If you have all 4 outputs active, and your Monitors are arranged such that the Primary output of card 2 is connected to monitor 3, then it's GPUID=2."