I rendered 4 takes in 3D MAX to 4 avi files using DivX 5.01 codec (1-pass quality based , keyframe every 15 frames) and they look ok and play smooth. The problem is that when I try to put them together in a single movie it starts to "jump" (it looks like a small skip forward) every keyframe, at least I guess so because the "jumping" occurs twice a second and my FPS is 30. I tried AfterEffects,PinnacleStudio and VideoPost in 3D MAX but it all looks the same. Even a single smooth playing movie pasted into editor and rendered to another file (using settings mentioned above) gives this jumpy effect. What am I doing wrong? It has never happened to me before. I tried my older animations and they work fine but I have no idea what coded did I used back then. Maybe I should use other than DivX 5.01?

Im am wondering if the original has no audio track? You may be adding one?
If this is the case AVI's can get skippy if the Audio/Video interleave is incorrect. Even if there is no sound you may still have a soundtrack that is blank causing this?

Firstly I would avoid using a non single frame format such as Divx for your source avi. Ethier RAW or a compressed lossless format, if your desperate for space an MJPEG format set very high quality would be my next choice.

virtual dub is also a handy free tool you might like to mess with

I would prefer to render you scenes NOT to the DivX file format.
Never make your raw material compressed!
Make it uncompressed, so nothing will jump. After joining it you can convert to a smaller video codec like DivX...