Similar to problem I experienced early on - see my post on IIS 6 . . .
I think you will find that if you turn error reporting on in the php.ini, (uncomment the line for error reporting) that you are still having problems with the php_mysql.dll file, and requests for moodle return the line
Fatal error: Call to undefined function mysql_connect() in c:\Inetpub\wwwroot\moodle\lib\adodb\drivers\adodb-mysql.inc.php on line 337
So there is a problem we are both experiencing relate to enabling the php_mysql connector.
Unfortunately, there is no current documentation for IIS and Moodle.
I will work on this - post replies if you come up with a solution.