Description:
------------
Consister the following setup:

You keep your source code in "C:\Repositories\example.org\trunk".
You just point your DOCUMENT_ROOT to that folder via symlink/junction:

httpd.conf:
[...]
DOCUMENT_ROOT "C:\Sites\example.org\htdocs"
[...]

C:\Sites\example.org>dir
 Volume in drive D is System
 Volume Serial Number is E49D-A2E7

 Directory of C:\Sites\example.org

2010-05-31  01:08    <DIR>          .
2010-05-31  01:08    <DIR>          ..
2010-05-31  01:08    <JUNCTION>     htdocs [C:\Repositories\example.org\trunk]

You now run the script "C:\Sites\example.org\htdocs\test.php".

Test script:
---------------
<?php
echo 'File: ' . __FILE__ . PHP_EOL;
echo 'Dir: ' . dirname(__FILE__) . PHP_EOL;

Expected result:
----------------
File: C:\Repositories\example.org\trunk\test.php
Dir: C:\Repositories\example.org\trunk

Actual result:
--------------
File: C:\Sites\example.org\htdocs\test.php
Dir: C:\Sites\example.org\htdocs