Oh wait! If you're running vista, take a look at the special Windows vista forum.
http://www.subsim.com/radioroom/showthread.php?t=105144
Read the last (beginning) page
http://www.subsim.com/radioroom/show...27&postcount=1
If your computer has Windows XP (I have a MacBook Pro" with BootCamp so I can run Windows), try to format and start with a fresh new Windows XP installation.
I really cannot understand that you're unable to run SH3!?! You don't need Service Pack 3 ... puzzle for me?
If you format, don't install .net from Windows and you will see that all will works fine.
Good luck!