Service Unavailable occur on my IIS+PHP(ISAPI)

[surfchen]

I down the php4 zip and unzip in c:/php

then I copy the php.ini.recommened to C:\WINDOWS\ and rename to php.ini

then I modified the extension_dir = "./" to extension_dir = ".C:\php\extensions"
and the session.save_path = /tmp to session.save_path = C:\php\sessions

then I copy the c:\php4ts.dll to C:\WINDOWS\system32

then I add "PHP" "C:\php\sapi\php4isapi.dll" to the ISAPI filter

the I add the ext to the Home Directory->configture(".php" "C:\php\sapi\php4isapi.dll")

then Iopen up the IIS Manager, go to Web Service
Extensions, choose "Add a new Web service extension", enter in a name
such as PHP, choose the Add button and for the value browse to either
the ISAPI file then check "Set extension status to Allowed" and click
OK.

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but after these steps,I run the PHP scripts,the browser said:"Service Unavailable"

I am puzzled~~~

I don't know who is fool~~

IIS or Me.... :mad: