well firstly i think that you need your text input to be in your form tags - it's sitting outside them at the moment.
Secondly, where are you gettnig the other values for teh select box from? If you want to add values to it dynamically then you'll need to store them elsewhere, like in a database or a text file or something. Your add_ip2_html.php file then needs to take the text you've entered, stick it into the database with the other values, and then you can reload the first page selecting all the entries from the database for the select box. I dont think you can make the php add more php codes into a php file, as it were - you need to make the populating of the select box a dynamic process.