I replace the battery on my 3G(which was lasting like 45 minutes), and I had to end up getting a knife to get between the plastic and the metal. If I used the tool they gave me it mashed the plastic in so bad, that it was starting to piss me off. So then I got a small pocket knife and made the metal separate from the plastic just enough to stick the "special tool in" (Screwdrive for a pair of glasses).
Then you just work your way around and push and pry, then it's open, kinda scary but it was fairly easy. Just make sure you start in the right place. The directions came with the battery, but I googled for it and found much better directions. Hope this helps.