Think DivX 5 is about the only thing on your list that has a mac version.
DivX 3.11 = hacked MS MPEG4 V3 which was for windows.
DivX 4 was basically open divx which was cross platform, so it should be possible to compile libs for OSX. Creating say a quicktime plugin is a different matter though.
XviD, once again is cross platform, but what you are used to would be the directshow and VfW front ends. For OSX you would have ffmpeg, mencoder, etc.
Nimo codec pack is a collection of VfW and directshow codecs/filters. The "W" in VfW stands for Windows and macs don't have directshow either.
dshow in FFDShow = direct show which we already covered. However FFDShow is basically a dshow and VfW wrapper for libavcodec and various other opensource libs. All of which you should be able to compile under OSX.
Tsunami = similar situation as Nimo.
By the way your really shouldn't be installing codec packs. Especially not more than one at once.
For the latest source you would need to do a cvs checkout. I assume that OSX comes with some kind of compiler standard so compiling shouldn't be hard.
VLC already includes libavcodec, libavformat, libdts, etc. For encoding I would also suggest you check out ffmpegX, an OSX based GUI for ffmpeg and other opensource cross platform utils.
What I meant about the quicktime plugin bit is I guess it (quicktime) is the mac equiv to dshow/VfW.
