I don't recommend using the Dritz pliers. They don't work very well, and the snaps available locally (and the ones that come with it) don't have long enough prongs to work well in diapers. The snaps are also *extremely* expensive to buy locally. For 12 "sets" of snaps, WM charges nearly $2.00. I have a pair of Dritz pliers and tried using the snaps locally, and with the exception of one diaper cover (that I rarely use and therefore rarely wash), the snaps all pulled out.
If you want metal snaps, I suggest buying the "Snap Setter" tool and the long-prong metal snaps that are available here:
http://www.thesnapsource.com/
If you need to do more than a few diapers, however, it really is worth it to get a snap press (or convert a drill press for use as a snap press) rather than getting the metal snaps. Long-prong metal snaps are $11 for 50 sets, while "plastic" snaps are $6 for 100 sets (or less, if you order from a co-op). The resale value of a snap press is *excellent*--people sell them for nearly what they paid new.