Post Video Production Software

I am looking for a relative simple video editing software that can remove the green screen background and let me drop in a still photograph in the background, and possibly a still photograph in the foreground.

I realize there are plenty of different programs that will accomplish this simple task but here is where it might get a bit complex. I use two (Canon HF100) HD cameras that produce a AVCHD file format. One of the cameras has a wide angle lens that captures a full body shot, and the second camera is set up to record simultaneously a chest shot. In post production I want to pan between the two camera angles.

I record the audio using a lapel microphone (Peavey PCX-U12) into a stand-a-lone digital recorder (Boss BR900CD). So I ultimately end up with 2 videos of the same presentation and a separate audio file. The reason I do this is because of the far superior audio quality I get with the lapel microphone into the separate digital recorder as compared to the any microphone you attempt to run into the video camera.

The post production software must allow me to import the separate audio file, and align this separate audio file with the audio file recorded in each camera. Once I have the alignment of the separate audio file set so I am essentially listening to one audio signal when the two video clips are playing I want to remove each of the cameras audio file.

In an effort to visualize what I am attempting to describe: I would like to see is two separate video files I will cut up to produce one video presentation, and three separate audio files, two of which (Video Camera Audio File) will get deleted.

If you are interest in an expanded explanation why I take this approach: Slide one of my presentation may be 1:30 minute video of me introducing myself, and welcoming the students to the course. Again, panned between the two different cameras. Slide two goes into Powerpoint because I require the visual illustrations of say a form. As my presentation bounces between video and Powerpoint, the same audio file is used to deliver a seamless audio file regardless if its me in a video or the Powerpoint.