Chris:
We have helped a number of people with Pronto remotes that want to expand to control home lighting. The Pronto is a great "front end" to a home automation system, but it obviously is not a home automation controller. It is simply an X-10 transmitter that will send X-10 codes (via an IR543) when you press the button. It can send a stream of X-10 codes however because of the macro capability.
So if you don't have a home automation controller to go along with your Pronto (like a Stargate), you might want to purchase X-10 receivers that have a lot of features built-in that don't require a home automation controller. One example is the PCS product line. It allows you to create up to 16 lighting scenes with an unlimited number of lights. Each light in a lighting scene can be programmed to a different dim level, and even how fast the light gets to that level. These features reside in the switch and don't require anything more than a single X-10 command to trigger.
As Carl mentioned, sensors that will detect the state of your A/V equipment are avialable, but they work with a home automation controller that has IF/THEN logic.
Please send me an e-mail if you would like us to help you select some equipment to get started.
Robert
RCI Automation
rciautomation@compuserve.com[Link: ourworld.compuserve.com]