Some time ago I created a gimp perl plugging to extract the dominions:PPP images from the files.
I was able to get the item files almost pefectly, they just were stored with no compression, 1 byte per pixel using 2-3bits per colour channel (or just got lucky with the colours).
IIRC the unit files had some sort of pallette and a kind simple of RLE. I got the centurion (was the 1st one) mostly ok from the 1st army.trs file, the other files used another set of colours.
The script got lost in a format&write-wrong-partiton accident so was never posted anywhere...
So start your hex editors to check the files and show your ninja coding skills.
http://en.wikipedia.org/wiki/Run-length_encoding