If the OP hasn't had much soldering experience before, it's definitely a good idea to practice on a junk board of some kind (a great use for discarded PC motherboards).

Once you get the hang of it, make sure that you work on the Mac's board with it secured mechanically somehow, or you risk the sort of tragedy that JDW cautions against. If you do this, and work carefully and deliberately, you shouldn't have any big problems.