My posting @ https://answers.launchpad.net/ubuntu/+question/101990
I tried your method and it worked. I have been playing around to get such result for two days. Well, actually there is a little bit of story before I get the result that I wanted. So, I tried some other similar method to Curtis', in my VirtualBox Ubuntu Guest OS. The strange thing is I kept getting problems. The X did not start, and the virtual console resolution got big and too wide.
I had a feeling that I might get different result in "real" system. So, I installed ubuntu 9.10 and applied Curtis' method. It worked. I am glad. What I noticed is that the X is running in virtual terminal #9 (instead of #7). No issue.
I have another method though. During my search, someone mentioned about 'nodm' for automatic display manager. Neat! Yesterday I tried it on VirtualBox with no success. Today I tested it in "real" system and all is well. I really recommend this method.
During 'nodm' installation, I had to remove existing display manager(s) first. Then, set the proper configuration in /etc/default/nodm. Enjoy!