The only solution i can offer isn't quite as simple as you'd like. It involves saving the flv files from youtube via http://keepvid.com then for conversion i use a linux script that basically converts the flv files to the required format (my preference is XviD).
I can't remember what format is required for the Vision M as i'm not interested in watching videos on it (that's what PC's are for), though i did test the few that i converted with the above script.
edit- the Vision M uses these formats 'DivX 4, DivX 5, XviD5 , MPEG-1 , MPEG-2, MPEG-4, WMV9, MPEG' so basically everything except flv files.
Other than that i'll wager it's as simple as googling 'convert flv xvid', that'll bring back dozens of programs, most of which get spammed here on a daily basis.
edit- anyways, just had another idea, the keepvid website i mentioned above allows saving of youtube videos in the MP4 format - there you are - job done..no messing with conversions..
