I watched this show on the Discovery Health channel one time, i think maybe it was Body Challenge, or something like that, where they were trying to improve this volleyball player's vertical leap. To so it, they had her sqaut with weight and then jump at the top of the movement. But the problem is, its really bad for your joints to land with weight on your back, so they developed with dynamic weight thing where once you reach the top of the movement, the weight it taken away so you can land with just body weight.
I dont know if regular squats will help vertical leap. You might have to actually do something that is like leaping in order to improve it....
-Fatty