Firstly, the files that look "encrypted" aren't encrypted, they are actually compressed with an EA algorithm called refpack.
This thread:
http://www.derelictstudios.net/forum...howtopic=15016
contains links to a number of programs capable of decompressing this compression.
As for the unit data and stuff, it is all XML which has then been compiled into binary format to speed up loading. (the binary data is inside various files inside demostreams.big) Modding C&C3 in any real way is not going to be possible without the source XML files (which EA will need to provide)