As above, it's not more than a days work.
After the bearings on my first axle gave me huge camber on one side, i put the axle from my donor on.
The hardest part by FAR is getting all the brake lines etc off in one piece. The threads (being a 13 year old car) were rusted to f**k and as the axle was no good anyway, i simply cut the brake pipes off and put in new unions where the pipe goes across the car behind where the axle sits.
The axle itself is a piece of piss to remove and refit given you've got a decent amount of upper body strength and someone to nip the bolts up while you're under the car; there are 4 bolts which hold it on:
One each side in the boot, one each side under the rear seats. Undo said bolts, it will come off. To get it back on, move new axle into place (or near enough)
Get under car, bench press axle into place, fit bolts into holes, have someone nip them up hand tight. Support axle with a couple of jacks or something similar, torque bolts up.
Put brake lines into new axle, *remembering to put load valve back on PROPERLY*, bleed brakes, jobs a good'un.
Soak the threads for the brake lines for a couple of days if you can, try and ease them off bit by bit. Be sure to use a proper brake line spanner as normal spanners will chew the thread. Failing that have some copper pipe and some unions at the ready.
If the brake lines cooperate and you have someone handy it shouldn't take too long at all!