The server displays the error pages, not PHP. Its not that hard to customize, and you can have a script do it, but once the misconfiguration page is being shown, your configuration is screwed up anyway. This kind of error usually results from your script not interfacing with the server correctly (like not sending the response code in the right format).

=\ I've been talking to HostGator support for 30 minutes and all I've managed to get from them is "500 errors are caused by too many processes running at once." Wow, thanks HG for that little gem right there. Sigh.