I screwed up though; I ordered the digitizer for a 3G, and I should have ordered one for a 3Gs. Not MITB's fault at all that the screen didn't work. So it's very important, when ordering, that you're sure what model of iPhone 3 you have. The screens are exactly the same size (see picture 2 - it looks fine), but the connector inside is slightly different.
If you're thinking of replacing your screen, but a bit worried about how difficult it is, don't worry! It's not that hard. You need a very small Philips screwdriver (I bought a set of tools from MITB) and a rubber sucker for removing the screen. To replace the glass, you only need to remove a total of 8 screws. Much easier than replacing the iPhone 4 screen. There are loads of videos on YouTube that show you how to do it.