Most of the time it’s not a codec problem, but a video hardware overlay problem. Make sure you have the latest version of the drivers for your video card, and the latest version of DirectX. If that doesn’t solve it, find out which codec is the culprit (by feeding the files that behave that way into a diagnostic utility like gspot, avicodec, or videoinspector). If it’s xvid, there’s a box in the xvid decoder options (assuming you have koepi’s build) that allows you to flip the video (nifty trick in my opinion). If it’s another codec, or all codecs in general, try disabling hardware acceleration (see http://www.moviecodec.com/topics/4454p1.html for instructions on how to do that)
I believe FFDShow did the trick. 'have’t used it in a while.
The following file will flip video and a lot more. It had too much stuff for a beginner like me. ACEMCP603PRO.exe It was on http://www.free-codecs.com , too.