Well the specs are on xentax,
http://wiki.xentax.c..._MotorSport_CAB-that should save you having to figure out the format from scratch.
To repack the files you will need to code your own app, unless someone here shares theirs (unlikely).
I recommend using Delphi if you are a programming newbie &/or you want a gui.
Otherwise check out C++Builder/Dev-Cpp/VC++.
You will need also to get zlib, for delphi you could use this:
http://www.dellapasqua.com/delphizlib/I'm not sure if there are crc's/zlib version checks in the xbe for the cab files, there are for the ca2's.
If there are you will need to patch these (Not easy, unless you are good with assembly).
Of course if you don't want to use the modded files with the game you don't need to worry about that.
Have fun,
KM
Note well what he has said here because i know that he knows what he's talkng about and he's dan good and unlike every1 else here that just talks he will give u advice and maybe some help along the way oh and ill also take a look at this stuff
it shud be interesting lol.