How can I make rows and columns for Spaces in Lion?
I’m pretty certain that you can't; you just get a single-line.

From John Siracusa’s review of Lion (when describing the implementation of spaces in Mission Control):


  The biggest limitation of this new arrangement is that Spaces are now confined to a one-dimensional line of virtual desktops. Four-finger swiping between spaces feels great, but there's no wrap-around when you hit the end.