I think Vegas properly checks the MPEG headers and won't load a .m2v file, regardless of the extension. So just renaming it won't fool Vegas into thinking it is an audio-less MPEG Program Stream file (.mpg, .m2p, .ps, etc.) or Transport Stream file (.mpg, .m2t, .ts, etc.). Although it accepts all other forms of MPEG files readily enough, even .vob files.
