Basic Video Editors that let me edit ".mp4" or".flv" videos

For a one time only thing, I need to do a short video.

The problem is the format are all strange: avi, mp4, flv, and mpg.

Is there a video editor besides Adobe Premiere (my system can’t run it) that will let me edit the videos? I just want to put some clips together and add one music track for a short presentation.

Sony Vegas.

Make sure you’re using ffdshow video decoder.