I have been experimenting and test running minimum install of the Ubuntu distribution - main base packages only with out any window manager ...
It is like running hard core Ubuntu from scratch and then build you own Ubuntu distribution and customize like you want to have/run things.
1) First you download Ubuntu server edition 12.10
Then you install the Ubuntu system with out choosing any additional packages or server options (just leave does empty) ...
Now you get a minimal working Ubuntu system.
2) Now you install the minimum to get things up running with graphical interface.
Now you have a minimum Ubuntu system running with Fluxbox.
sudo install xorg
sudo install xdm
sudo install fluxbox
That was easy and you can do it with any window manager you like.
3. Now you can install all the softwares you like running.
For inspiration you can take a look how other tiny linux developers solve there distribution with light softwares picks - like puppy among others.