Here's something semi-relevant:
http://www.awesomefilm.com/script/Alien3.txt
William Gibson wrote a script for Alien 3, which unfortunately got rejected. The basic story is that some evil firm creates an airborne virus that causes people to turn into Xenomorphs (or something like that - I haven't read the script for over a year)
The most detailed TF is the first one, about halfway through (Ctrl-F for "Meeting of Anchorpoint"). It's a female TF, which is good, however it's one of those gory "bursting out of the skin" things, which might not be everyone's cup of tea.
Edit: On another note, I'm surprised there haven't been more Alien TFs around here. Maybe they're just hard to draw?