Are you looking for an interactive lesson to investigate the angles that are created by parallel lines and a transversal. This might be the lesson your are looking for.
The main file for making this lesson interactive is Geometer's Sketchpad. If you have that computer program, then this is the activity your are looking for.
This zipped file contains a Geometer's Sketchpad file where you can change the parallel lines and the transversal and notice how the angles change. The zipped file also contains a full set of lesson plans (and directions for using the sketchpad file), student activity sheets, problems for students and an assignment.