uhm sounds like you are thinking that you can modify the cs2d max engine since you're talking about switching between directX and opengl mode (menu concept drawing). this would only be possible with the cs2d max engine. the old blitz 3d engine supports directX only.
however you just can't mod the cs2d max engine. it's closed source.
Read the description. The L4D2D will use completely new engine which I will probably code (but it's not sure) after TF2D. Maybe I will use BlitzMax for that if Aceman really wants DirectX and OpenGL mode.
this thing will never happen, it has been 7 months already and still 0% complete, that sucks.. i wanted to play it, to bad..
next time if you are going to make a game, be sure you will have time to do it
because if you leave the work and dont finish the game, users (like me) who are waiting to play the game get disapointed and you guys never release it..