I've done a minimal ubuntu install (12.04) on my old laptop. After it installed the core system I told it I wanted to manually select packages.
Then at the terminal prompt I installed lxdm (which install lxde too) and network-manager.
(sudo apt-get install lxdm network-manager)
That all seemed to go ok, but now I can't get lxdm to start up on boot. What's the problem?