I got this silly idea in my head that I wanted to use two monitors, both displaying different things, at the same time. It doesn't work on the computer I usually use, either in Ubuntu or Windows (the computer dual boots). I tried it on my other computer, which I don't use because the hard drive is dead, using an 8.10 live USB. It worked.
I got excited and installed 9.04 onto a 16 GB flash drive. It's not a live USB, it's a regular install on a flash drive. I am able to boot that computer from the flash drive.
The second monitor doesn't work while I'm logged in. I go into the display settings and the second monitor is set to off. I click to turn it on, and it says I need to log out and back in. I log out, see the login screen displayed on both monitors, and when I log back in, the second monitor is off again.
The laptop's screen is recognized as laptop 15" and the second monitor is recognized as Hewlett-Packard 20".