Best Software for editing MP4 Files?

Just bought a FLIP Mino HD Camcorder but the editing software that comes with it is very limited. Problem is that the MP4 (not Mpeg-4) files are NOT supported by my two video editing programs (Sony Vegas, and Windows Movie Maker). Anyone know either an easy conversion program OR software that can handle Mp4’s? Much thanks.

Um, MP4 is Mpeg4.

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