Here's the poop: A halogen bulb (not the fixture) is still an incandescent load. As long as the bulb is 120v, and not 12v (i.e., no transformer), any dimmer of the proper capacity will work fine.

The problem here is with cascading dimmers. Usually, as long as the lamp's built-in dimmer stays set fully on, there is no problem. Better still would be to bypass the built-in dimmer.

Joe is correct about dimming halogens, to a degree. As long as the light is used at full brightness occasionally, the reduction of bulb life is minimal. You should get better than 75% life.