I totally endorse what Charlie McG says about Sony Music Movie Studio but say that the only drawback is a mere 4 video tracks!!! BUT as I am not James Cameron this is not much of a problem.
I bought a copy yesterday and lost 5 hours as I played with it going "WOW" I found I could do some amazing things without once looking at the manual !!
I am now working out how to do "green screen" stuff and also reading the manual
Also there is an open source program WAX to play with which can be used as a plugin with the professional, and far more expensive, version of Vegas. Sadly not Movie studio.
Also just downloaded, but not played with Zwei Stein which says it can "edit up to 256 video, audio and still image clips, each with up to 64 effects chained serially".

Why is there only 24 hours in a day?