What I'm mainly interested in is the mission .txt and .dat files, these
are in the DATA subdirectory of the game directory. With the online purchased version I have,
most of these files are compressed and unreadable. There are two files for each mission, one
with just the mission name (e.g mission1.txt) and the other with "-mission" after it (e.g mission1-mission.txt)

The first file contains basic data such as weather and player ammo loadout, and is uncompressed. The second one (presumably) contains the actual mission data, such as vehicle types and placement. This file is compressed with my version.

I believe the .dat files contain information for buildings, trees etc; not sure if these are uncompressed in the CD version, or if they are just binary files.

I'd be interested to know whether the mission .txt files for your version are compressed or not.