Ubuntu Installation :: Changing Computers - Cannot Add Repositories

I'm in the midst of updating from my poky old Dell to a newer (3 yr old) HP laptop. I've completed most of the changeover, but I can't seem to add any repositories to Software Sources. When I attempt to enter the APT line into Synaptic, the only button that's clickable is "Cancel." This holds true even if I use sudo to run Synaptic from the command line.

I've also tried editing /etc/apt/sources.list directly, but when I enter the corresponding lines (cut and pasted from my old computer, to eliminate the chance of typos), I get a message that the newly inserted lines are "malformed."

I'm sure I've overlooked something simple, but I've been at this for two days now and I'm getting a bit frustrated (doesn't do much for mental clarity).