the problem is not the player as such by the sounds of it but the codec.
It sounds like you are decoding using ffdshow, however, older versions are incompatible with Xvid. Load up windows media player 6.11 (in windows media player directory, called mplayer2). Load up your xvid in the player, then go to file>properties>Advanced>ffdshow>properties and uncheck xvid playback.
You will get good quality in everyplayer. If you have a problem, use the board search for ffdshow. There is lots of information about this problem already, it's very common
BSplayer is a good player, although I prefer zoomplayer.