First time I've hard of the .MV file format but it does look quite impressive.
I've found
AVI-Mux GUI (downloadable from
http://www.alexander-noe.com/video/amg/) which is a freeware software licenced under the terms of GPL.
I've opened it and it looks like it will let you output to .AVI.
Try that and let me know if it works or not.
I'm going to try downloading some samples and playing around with it.