DIfference between ISAPI and CGI

Hi all, I installed some months ago a Win2K server with IIS5 and PHP4; I have some crashes on IIS/PHP (I can't understand who fails) and I get "PHP encountered an access violation .....". This happens about 4/5 times a week; I read that this can be caused by the ISAPI module that I installed and many of you suggest to install the CGI instead. But now the problem: when I set the PHP.EXE instead of PHP4ISAPI.DLL, I got PHP working, but he doesn't find the MSSQL functions (like mssql_connect()), when it was full working with ISAPI. Is there some changes to make to php.ini file? I repeat: with ISAPI it was working great (except, of cource, the random hangs). I only changed the executable in the IIS management console. Thanx to all. Fabio