Geez, guys, all the features are clearly on the Specs page at the Apple website.
And yes, if you want wireless at home, you get Airport Express. Unless you have 49 brothers and sisters, you don't need 50 connected users on one wireless station. Business may need it, though.
Anyway, Airport Extreme is a wireless router, while the Airport Express isn't necessarily a router, although more than one person can connect to the internet using it. It may not assign each user of Airport Express their own IP. I believe a router is treated like a single computer connected to the internet would be treated --- it's given an IP. If the router is given an IP, then all the computers on it are given similar IPs, but slightly different so that each computer using the router is known. However, I don't think that's what happens with Airport Express.
I don't know much about networking and stuff, so I hope that someone can clarify and tell me if what I said makes a lick of sense.