I'm having a similar problem, only i didn't try to set up virtual hosting. Only experimentation server on my own computer where i can use loopback to test: http://localhost/exp/fun.php
The problem is: php code is not parsed as code, but transfered directly as a Processing instruction, just like <?xml ?>, for example. That's why nothing is visible on the browser.
Some installation details:
Apache 2.0.53 from windows installer.
PHP 5.0.3 or 4.3.10 from zipped binaries (both had the same problem).
I did everything the manual said. PHP is extracted to C:\php. The Apache installer extracted everything to C:\Program Files\Apache Group\apache2.
I added to httpd.conf AddType, LoadModule and PHPIniDir just as the manual said. Also that php4ts.dll was copied to apache2\bin directory.
The problem still existed after adding c:\php to PATH, copying php4apache2.dll to Windows\system32 directory and php.ini to Windows directory.
Also, i'm on a home network. Two computers with one internet connection and the regular windows Internet Connection Sharing. I don't know if it has anything to do with it, because the first apache Test Page can be seen. Only php code between <?php and ?> isn't being parsed.