Apparently my serial port is broken on my primary laptop, because when I first connected and powered up the Gumstix motherboard, the output was pretty messy. But when I connected it to another laptop everything looked fine, and I could log in on the machine.
I connected the ethernet cable, but could not get the network interface to work. It just said eth0: link down.
Googled and found this: netCF-ethernet-problem. It turns out that the firmware the motherboard shipped with has a broken ethernet driver.
So I'm now rebuilding the system, which takes quite a while.