Questions on combat in 3d space

[frogglesmash]

First off any tips on how to make the use of flight during combat more streamlined/easier to use would be great.

Now to the main issue: How do you determine how much volume a creature occupies in 3D space? Are creatures assumed to occupy perfect cubes that are based off of the area they occupy on the grid, and if not how do you determine the volume they occupy?

[Rebel7284]

Same as with ground combat, all characters occupy a cube based on their size. They don't have to physically take up all the space, they are assumed to constantly be moving/dodging/weaving within that space.

[MilleniaAntares]

Bipedal creatures are taller than the other types. Humans take up 2 vertical squares, while a medium dog takes up 1. Horses are 2 squares high, while a troll is more like 3?

d20srd.org has a height chart. I can't access it right now, though.

Edit: Here (http://www.d20srd.org/srd/combat/movementPositionAndDistance.htm#bigandLittleCreatu resInCombat) is the chart.