First, the premises: PHP loaded on IIS6 on Win2003 STD R2 SP2, PHP_5213 using FastCGI, MySQL_5145.
Customer sent me the site files, which I unzipped to C:\\InetPub
C:\\InetPub
Edit your php.ini file and set the display_errors and display_startup_errors options to On so that you can have a chance to see what the problem is.
php.ini
display_errors
display_startup_errors
On