Expose

I am a long-time Mac user but new to OS 10.5.8 and Expose. Why is Expose so jumpy? It changes window sizes even if the mouse is perfectly still and also with certain mouse strokes which I have not been able to identify. This is driving me crazy and costing me a lot of time. Also the F3 key activates Expose, but F9, F10 and F11 seem to do nothing related to Expose. Can I completely disable Expose? Spaces is not set up yet.