Soldiers will not shout you:
     Go  project  IGI  installed folder then goto commen\ai backup the
folder  ai, There will some files like "civlian.qvm" ,"guard.qvm" like
that  names of enemy's copy the file "civlian.qvm"[ctrl + c] and paste
it[ctrl  +  v] in that same folder, if willbe like copy of civlian.qvm
then  rename enemy's files into some other names then then rename copy
of  civlian.qvm into name of enemy's files like guard etc.. then start
the  game  then enemy's willnot shout you or kill you ,If thay see you
than thay will run away like civlian.

     There's  a  secret  gun  in  the whole game and it is on the last
level  behind the crates as you kill two guys right and left with spaz
12 and open the door to the crate room and the gun is colt anaconda!