Some of the WMV's i have got lately dont work when i try to conver them, i had a thought that if i use Windows Movie Maker (u get it in Windows ME) dont know about other stuff, but i added the whole video file to it and converted the downloaded WMV to WMV again using Windows Movie Maker

then i tried to use TMPGENC to encode to MPG and i had sucess, no audio/video sync problems..

hope this helps