It's generally cheapest and easiest to just get a wheelset.

Places you can get wheels include:
PricePoint
Cambria Bicycle Outfitters
Bicycle Wheel Warehouse
Universal Cycles
Wheel World
Performance
Nashbar
Chain Reaction Cycles
... the list could go on for some time.

Check out some local shops if you have some nearby.

Now, As for hub replacement, if you really wanna get in over your head, get a hub with the disc mount you want and the same number of spoke holes as your rim and has the spoke holes about the same distance from axle centerline as old hub (so that you can re-use same lengths of spokes).

[insert wheelbuilding link here]