NOthing related to crossover's is basic.. I wish I knew a lot more about this stuff so I could give you some answers. Big reason why my next project will be an active network -- I know I'm not smart enough to figure out the crossover bit.
Anyway, I've got some links that may help you.. use them as you see fit.
Link 1 Link 2 Link 3 Link 4 Link 5 Link 6 (Has a basic calculator in the middle area)
JCD