Plug them both in, and then use the Catalyst Control Center (or Window's screen settings menu) to arrange the monitors how you like.
I was pretty sure that it would be that easy but wasn't sure. Now that the price of monitors is going down, a second 17" will be nice.
BTW, how do I open different programs/documents on each screen? Do I have desktops on each and I just select what I want on each screen? Thanks!