depends what you're trying to do.

Final Cut Pro for the mac, Adobe Premiere for windows are both good choices for most movie editing, and will give you a lot of options which will probably let you do what you want.

If you're just trying to throw away the original audio track and mux in a new one, you could use virtualdub for that. If you're trying to actually alter the audio track, you could use virtualdub to demux it and Audacity to edit it.

All of them have learning curves, but none of them are insurmountable.