Okay, well, I finally got my hands on Birthright... and unfortunately, I can't tell you much. The .RES files definitely contain the graphics, but unfortunately they appear to be compressed. The good news is that it's not a very heavy form of compression since I can kind of make out distorted images in the data, but nothing will resolve itself into proper images. The palette data is stored as .COL files under /GRAPHICS/ on the CD in 3 bytes per pixel format. I do find it INCREDIBLY interesting that the map format is exactly the Doom .WAD format, right down to the maps even using standard Doom names when opened in Doom Builder 2. Is this a licensed use of the Doom engine (or at least its underlying technologies) that we've never heard of, or did somebody at Sierra do a little bit of reverse engineering?
If anybody with a little more skill in this sort of thing wants to check it out, I'll upload one of the smaller .RES files. Hopefully somebody will be able to crack the compression algorithm used on them; like I said, it can't be too complex since I can definitely see where some of the graphics should be showing up.
EDIT:
TEXTURES.RES for anyone who's interested. I've checked a number of files in hex editors to see if I could find any sort of clue as to what kind of compression it is, but with my limited knowledge I came up with nothing. Surely somebody else can do a better job than I.