I have no idea what the problem is. ha
You have PHP4 install? You have a customized .htaccess setting to allow you to run both side by side? Cause DH sure doesn't do that for you by default.
What's the phpinfo() for both?
You might say they are running side by side, but unless you setup your .htaccess file for it, I don't think it is. You didn't say anything in your post about adding custom file extensions to allow such a thing.
Need more details as to the problem before a solution can come about.
yerba# rm -rf /etc