Even if you are not using OpenGL, rendering 100 simple items shouldn't be a problem at all. Chances are you are doing something wrong. Try adding 100 pixmap items and see if that's slow. If not you need to show us some code, or at least a screen shot of the kind of scenario you are creating (how big images. how many are visible at the same time...).
And another thing. Why is moving the mouse slowing down your app? Are you reacting on hover events?