i made some corrections at the desert tileset. i flipped some objects which were shaded from the wrong direction and fixed some missing pixels at the big sign.
you should maybe check if i haven't screwed up anything while doing so before you replace the version in the cvs.
You seem to have messed up the shadow of the two stone tiles at the top of the desert1.png set a bit. Couldn't you just mirror the originals completely instead of trying to mirror just the stone? Also the small stone next to the medium one disappeared.
In general modifications are fine but I think more should be improved about these tilesets before committing it to CVS.