I have a batch of texture files for heretic that makes the appropiate textures transparent, if you are patient enough I can upload it to my web space, but it might take some time, my desktop computer has a fan problem now and I don't want to use it until I fix it <!-- s:( --><img src="{SMILIES_PATH}/icon_sad.gif" alt=":(" title="Sad" /><!-- s:( --> (which shouldn't take long).
I fixed them using Paint Shop Pro, I created a background layer for each of the images, that made the trick.