Well just to let you guys know: I started looking into the animation files a bit.
I already wrote a python script that can extract them from the .idx/.dat file - it seems they aren't packed or anything since Verci's old cas importer was able to import them (well they didn't work properly, but it didn't crash, either).
So what I'm planning to do right now is to figure out how the .cas files are described by leeching a bit of know-how from the cas importer :P
As for the idx file (only pack.idx):
It has a header consisting of the string "ANIM.PACKV:|", then a long 9 and then a long with the number of entries.
Each entry then consists of:
Bytes Variable type Explanation 0-3 long strlen+10 of the tag (below) 4-7 long byte offset in pack.dat 8-11 long byte length in pack.dat 12-15 float Unclear so far, often 1.0 (first four additional bytes of the strlen+10) 16-25 - These are the other 6 additional bytes in the strlen+10* strlen String tag (qualified path for the animation)
*They seem to be 0x3F**00140014 - 0014 is 5120 as a short which sounds probable. No idea about the first two bytes.