Well, after some RE'ing, I've figured out the EQ2 VPK archive-ish format.
To do so, I wrote a very basic script that seeks out zlib deflated segments of a file and gives their length (in python, based on my php version; it's available at
http://home.archshadow.com/~daeken/find.py)
After looking at the output when run on a few vpk files, I realized that there are 4 bytes before each compressed segment. I broke out my hex editor, and found that those 4 bytes are the length of the segments. Score.
So the file format is as simple as this:
Read 4 bytes from the file as an unsigned long in little-endian (x86) format.
Read that many bytes from the file, and attempt to zlib inflate it. If it succeeds, write the decompressed contents to your output file, otherwise write the original data. This is how SOE managed to make both compressed and non-compressed VPK files
Repeat until you get to the end of the file.
Happy Hacking,
Lord Daeken M. BlackBlade
(Cody W. Brocious)