Tha Haynes repair manuals have pretty good wiring diagrams in the back of them. If you dont have one, you might want to buy one and keep for future repairs.
You basically need to find the wire that goes from the dimmer switch to the bulbs that are controlled with it, and tap into that, but to do it right, you got to find the wire, and without the diagram, it can be very frustrating if one does not have alot of expierience.