Tools:
DivX Codecs( http://divx.com/ ) and a movie.
DivXG400 http://www.tac.ee/~prr/divxg400/ (good program thou)

Note1 this is not a fix more like a discovery.

1.Open your movie with mplayer2(playing or not playing), right click mplayer2 goto "properties" or "file" then "properties".
2.Click on "Advanced" tab, click to highlight "DivX decorder Filter" goto properties or double click "DivX decorder filter".
3.Click "Quality Settings" and check "overlay extended mode", click ok for "update directshow status", then ok again.
4.Rather then completely closing out, return to "Divx decorder filter....quality settings" choose your "Aspect ratio".
5.Now click ok, ok agian, then close, then "alt-enter" for full screen mode.
6.If not the desired effect, return to step 1 then 4, select something else.

Note2 if changes have not taken effect, completely close mplayer2 then relaunch it.

1:1 = Narrow Screen mode(Vertial borders)
4:3 = Full screen mode(No borders)
16:9 = Wide Screen mode(Horizontal borders)
Maintain Original = Default

So Enjoy.