I just asked this question (Using External Monitor and Spaces. Want Mouse to move Up/Down, not Left/Right?) and @calavera gave me a great answer, thanks!
But now I have another question. It seems that the menubar wants to stay with the laptop and doesn't seem to be possible to move to the external monitor. Am I beating a dead horse here or is it somehow possible to achieve the layout I'm looking for? See screenshot:
(source: mikeschinkel.com)