In order to get PHP 5.2 stable running on Windows Server 2003 x64 (IIS 6.0), I discovered three things (in addition to the other comments above):
* Some PHP web applications make use of the SCRIPT_NAME server variable which is not available under CGI. You have to use php5isapi.dll, which is a 32 bit dll, so you have to run IIS in 32 bit mode. Confer http://support.microsoft.com/kb/894435. This applies to all ISAPI extensions and not just ASP.NET.
* It appears you must leave the doc_root entry in php.ini blank. At least, that is what finally made my installation work. (Note that others have suggested to set it to e.g. C:\inetpub\wwwroot or equivalent. That won't work if your server hosts more than one domain, each placed in a separate directory.)
* If you are e.g. using MySQL you will have to edit php.ini. In order for it to be found, you must set the PHPRC system environment variable or the registry entry. Note that if you edit the registry using regedit.exe, the PHP key should be placed under the [HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node] key. This happens automatically if you set it using a 32 bit legacy application.