Well after looking them over. They both support Audio up to 320kbs in various formats. Apples AAC and Apple Lossless, AIFF and WAV will give better sound quality on the ipod being lossless codecs. For almost all of the other specs they are identical. The ipod 30g and 80g 5.5 are much thinner than the 30g Vision M.
The Vision M does have better support for more video formats, but lacks support for H.264 which is a much better MPEG4 format which the Ipod supports. Getting video into the MP4 H.264 can be a pain at times, but is getting easier since Itunes now supports conversion, although much slower then other programs like Nero Recode 2. There are also free programs like Videora which are faster. Video output is 640x480 for the Ipod and 720x576 for the Vision M although I don't know the player can play a larger resolution video. I know the Ipod can play the 640x480 video.
Topic should be moved to peripherals.