H264 MKV with AC3 audio to Xvid AVI with same audio

I have some .mkv files with H264 video and dolby Digital 5.1 surround sound (AC3) audio.

I tried AllToAvi and it worked but converting H264 .mkv’s it
converts the Video to Xvid-AVI the audio to Mp3 2.0 (stereo)

and it resembles it to 44100Hz and doesn’t keep the full range
of sound that you’d normally get from the original DVD

In any case I am looking for a vista compatible converter for that can convert an MKV with H264 video and ac3 audio to an AVI with Xvid and still keep the original AC3 audio can anyone help me With this

http://www.dslreports.com/forum/r19571065-SOLVED-ffmpeg-mkv-to-xvidac3

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