you can try to configure your server to parse the .php3 extension with the php4 module. I don't know if Server lets you do that easily or not. I don't know if it will even work right. I think it depends on the code, but its soemthign to try
in the /etc/httpd/httpd.conf there is a line that looks like this:
AddType application/x-httpd-php .php .html
(I added the .html, so I could parse php within html files)you would want to add .php3 to the end of it
.php .html .php3
YOu could try that and see if anything breaks. If it does, then you'll need to install the php3 module. and add that type to the conf file. Maybe this is automated in Server. If so, that's cool.
For better help with that, ask in the Unix section of this board.
* I edited this to make it more clear. I changed some stuff. MOre info
here