I don't think you can do what you want, taxigirl. If you ignore the speed control aspect of the units, they are basically just an on/off switch. However, to control a light (or whatever) from two locations, you need a
3-way switch instead of the simple 2-wire switch.
I'm not familiar with the specific unit you have, but my guess is that this is your problem. If they have a "3-way controller", this is what you would want instead.
Hope this helps,
WallyH