The treeview checkbox style requires Comctl32 version 4.70, which is not available on all systems.
OK, I understand. Which system doesn't include version 4.70 of ComCtl32 ? Why not make it a minimum requirement for NSIS Installer to work ?
Personnaly, I don't like to see Luna elements on a Win9x/NT/2000 platform... it looks bizarre.
Do you plan to fix it ?