Funny thing is: I can start all my Lazarus created apps (not as complex a Lazarus) with themes, but not Lazarus itself.
It seems that this is a problem "on the edge" and hard to find out. It's probably not a problem caused by Lazarus only, but a problem
of a certain cooperation of the Lazarus-IDE and GTK.
I can't imagine that my desktop computer hasn't got enough "resources" for running the Lazarus-IDE.
I can run all applications from Monodevelop, OpenOffice, Eclipse, KDevelop, Gimp to Kylix, even on my notebook, where it never worked (even without themes) on SuSE 9.0.