I created an application which is very similar to that. I'm unsure if there is a better way or not (probably there is)...but as the items get added to the listbox, I am also writing them to the ini file. That way when the application closes, you don't have to read all of the current values in your listbox.
Likewise, if you later create a "remove" button, you can have it search for the line in the ini file and remove it just as easily. This way, your listbox is always in sync with the file. Let me know if you would like to see a sample. I'd post it now, but i'm not at home.