Answer to "Headphone Jack Stuck on Digital Out"As much as I would like for there to be an easy fix, there isn't. The same thing happened to my MacBookPro. The toggle switch inside of the port is defective. The only true fix is to replace the Logic Board which Apple will do for free, it's a known issue. If that is not an option for you, the "toothpick fix" listed in the forums at apple may work.
Answer to "Internet connection through Ubuntu?"If you prefer a graphical interface and depending if you are using Gnome or KDE this will help you. http://www.ubuntugeek.com/ubuntu-networking-configuration-using-graphical-tool.html