If you use a junkyard CV then as mentioned above you can just replace the part from the inner joint out. You can probably do this swap in a few hours or less. If you use an aftermarket CV it probably won't match up with the factory joint so you would have to replace the axle shaft from the diff outward. This is a MUCH more involved project than the first option, probably take you all day or more, and you will want help to handle the center axle housing.

Here is a quick description of the outer swap:
1) Remove the spindle (disconnect upper and lower balljoint and tie rod).
2) Remove the band that holds the inner joint boot to the "cup" that is on the diff bracket and pull back the boot from the cup.
3) Usually there is a snap ring of sorts inside the cup. Feel around the inside perimeter of the cup in the grease for a groove that will allow you to get a small screwdriver under the snap ring. Pry out the snap ring.
4) Pull the old CV axle out of the cup and off the vehicle.
5) Pull the junkyard axle apart at the inner joint the same way you just did the one on the vehicle.
6) Reassemble in reverse order using the "new" axle. The snap ring in the cup is optional. A zip tie will work for the boot band on the cup, or get the special band tool at the auto parts store.