I haven't seen an answer to OP's question. All those tools mentioned except the BMW special tool in prior replies will fail doing this job. The ball joint is not machine pressed in. It's pressed in while you tighten up those 2 bolts that hold it. So, it's still a pressure fit. Don't think about removing them by hands after removing those 2 bolts. Weasel pointed out one tip - make sure your socket has good grip on the bolt. They're very easy to be damaged. It sucks when that happens.

The BMW special tool is actually similar to slide hammer. I don't think you want to spend that money on this tool (a couple hundreds). Now, here is the tip you need. Cost of this solution could be $0 if you can rent them from local autozone. If you want to own the tools, get them from place like harborfreight for cheap. 2 things you need - slide hammer(like http://www.tooldesk.com/images/close...TD-3045_lg.jpg 3lbs one is good enough) and tied rod/pitman arm puller(like http://4x4icon.com/offroad/063007_st...2645_small.jpg).

Put the pitman arm puller as the attachment on your slide hammer. Leave thrust arm on the ball joint but remove 2 bolts holding ball joint to the steering knuckle. The just use the pitman arm puller on your slide hammer to hold between thrust arm and ball joint. Give it about 2 strikes and ball joint should come off. If the ball joint is heavily rusted, spray something like WD40 or PB Blaster and give it a few strikes. Leave it there to let the fluid penetrate thru. Give it a try after a couple minutes and it should do the trick.

Here is another tip. Make sure you get the alignment done after replacing the arm.