CEGUI has two positioning methods. The unified positioning and absolute. with the unified system you can align the window to the left/right/top/bottom/center side und use an relative offset to define the distance to the border. you can also use exact pixel offsets, or a mix between relative and absolute positioning sizing is possible too. So yes, you can position your widgeds resolution independent - or, if you don't like this - not.
The premade skins are ugly, so I created a Win7 lookalike skin.