I've explaned this to a couple people befoere and the first thing I tell them is to get the video camera ready, it could be a priceless moment.
You'll need a friend to help, loosen the nut that holds the wheel on, but don't take it all the way off, Have a freind ready with a hammer and a drift or punch( I've used a 1/2 drive extension before). Sit in the helm seat and pull back on the wheel while your buddy takes the punch and centers it on the steering shaft, have him give the punch a good whack or two( hitting your fingers with the hammer earns extra points), it should pop the wheel off the tappered shaft. It make take some pretty good whacks and you need to put a fair amount of pressure on the wheel. Make sure to leave the nut on so when the wheel pops loose, the person pulling back on the wheel doesn't go flying backwards( this is where the video camera comes in). Ive had good luck taking salt encrusted wheels off with this procedure, give it a try.