Hi 

realpath($PHP_SELF);

doesn't give the same result as 

realpath('index.php');

While the result of the second example is correct, the first one outputs only part of the value, in my case:

Correct: d:\inetpub\wwwroot\blue\index.php
Result:  d:\blue\index.php

wwwroot is DOCUMENT_ROOT in my case. 
I use NT4/IIS with PHP as ISAPI (not in safe mode).

Christoph