Is it simple to make it so when you print a message it opens in a pop-up instead of a new tab?
Yes you could make a plugin that opens the print command in a new window.
I don't know how to make plugins :(
would it be easy? Im new to PHP programming. Is there anyway to add a javascript popup to the button link or something like that?
All the php part would do would be include the JavaScript file witch could then alter the print command to open in a new window. You could take a look at compose in new window plugin to get an idea of what it would look like: http://www.roundcubeforum.net/7-third-party-contributions/46-api-based-plugins/6259-compose-new-window.html