I am having trouble also installing a dual dimmer switch for my light and fan. I can only get it to work both at the same time. I have a three wire (plus ground) black, white and red going from the switch box to the fan/light. And I have three wires coming from the fan/light unit and three wires from the dual dimmer switch. What colors do I hook together?? Help!
Thanks,
Bill

With house wiring, white should always be the neutral wire. At the fan/light, connect the white to white, black to black, and red to red (assuming those are the colours). Also, be sure to connect the bare ground to the junction box the fan/light is connected to.

In the box where the dual dimmer is installed, connect the white from the incoming power to the white that feeds the fan/light. Connect the black from the incoming power to the "power in" terminal of the dual dimmer switch. Then, the other two lines from the switch connect to the red and black that feed the fan/light. You'll probably also have to connect the bare ground to the dimmer switch, as well as to the box and to the ground that goes to the fan/light.

The page below is a pdf for wiring a dual dimmer from lutron, assuming that it feeds two separate lighting loads:
http://www.lutron.com/techInfo/InstallGuides/030-891-12.pdf#search=%22%22dual%20dimmer%22%20switch%20wi ring%22

Where does your power supply (black/white/ground) connect, at the fan or at the switch box?

http://www.ceiling-fans-n-more.com/ceiling-fan-wiring.php