I acquired the screen for the laptop. I also got a usb current meter so I can determine how much current the whole setup is pulling. After changing the max usb output current an cutting a couple jumpers on the screen, I was able to power the screen through the pi. It turned out that the whole setup, including keyboard and wifi dongle, pulled less than 750 mA, or 3.75W. The battery that I am looking to get, and hoping will be as large as claimed, has about 57Wh, so the battery life ought to be around 13 hours, which exceeds my original goal.
I found a nice writeup from a fellow who was setting up a CLI only linux box (http://lcorg.blogspot.com/2009/02/project-building-all-text-linux.html) and used some of his suggestions, most notably the "screen" function, which is great because I often need multiple command lines open.
Now begins designing the case for the laptop. I can at least work on the front panel, which will need to hold the screen, a breadboard, and a socket for programming.