Do read probably, I'm not referring to fun-plug but AjaXplorer apps which is what this topic is all about.
To use an ajax that is not linked to the original firmware you need to install fun_plug , then get ajax packages . After that it's up to you to manage it .
Or, just get the Open source firmware (on D-link FTP server)and rescript all (but it's harder)
With an ajax fun_plug version you can create a real ajax server , which means that people can acces ajax directly (not using the DNS-320 login page)
Edit : all credits goes to Uli that makes a really good job.
Edit2: Sorry for my english , it's not my native langage