There's an oil seal on both yokes. When you pull the axle, your gear oil will drain out of the axle hole because there's nothing holding it in once you pull the yoke loose from the seal.

It really helps a lot to have a 2-jaw joint separator. That way you can easily separate the lower ball joint from the front suspension assembly without having to beat it to death with a hammer. If you use the separator, or a hammer to get it loose, leave the nut on the very end of the threads of the ball joint so you don't mushroom the bolt or damage the threads. Often times, the threads on the ball joint get destroyed if you hammer on them, and using a pickle fork will usually tear the ball joint boot.

Replacing the ball joint is even easier than replacing the axles if you have snap-ring pliers (to get the old one out) and a pair of welding clamps (to press the new joint in, but some people use a hammer and tap it into place). I got new ball joints for $18 each because mine were already hosed.