I am having (what I think to be) a similar problem. Running dual monitors, primary mon on the right, secondary on the left. The interface of any given theme is split into pieces between the two monitors. I would *like* to have the display on my secondary (left) monitor only, since it doesnt seem to play nice will full screen games.

http://www.litestep.net/index.php?section=4&action=view&catId=1&id=563
I have read this thread and as I am new to litestep, I am still unable to solve my problem, however I am willing to learn :). Here are some screenies of my problem:

(UniverseMetalLS) http://stapled.lbox.org/litestep/dual_lite_01.png
(Simplicity) http://stapled.lbox.org/litestep/dual_lite_02.png
(Chaos) http://stapled.lbox.org/litestep/dual_lite_03.png

Any and all help appreciated!