GE 18023 Dimmer Rocker OnOff with Slide White "door light dim" Questions

I want to install the 18023 ge dimmer in the middle of a 4-way switch already have a dimmer by the door but don't need it. I can't get the lights to all work unless the switch by the ...

...door, but no luck in dimming. Additional information: I have four halogen bulbs in my receding ceiling lights. Hi Sara, Please read this entirely before attempting. I am an electrician and would like ...