Agreed, Apple isn't very clear on the differences.
In summary, the Express can only handle ten users (not fifty like the Extreme), only has a single ethernet port, has no inbuilt 56kbps modem option but has AirTunes (an audio out port).
The Extreme can handle fifty users, has a second ethernet port for hardwiring another computer or network drive/printer but has no AirTunes.
The range and speed is claimed as the same.
So, for the majority of users, the
Express is a much better buy since it is so much cheaper.
Edit: thanks
fayans, the Express is cheaper than the Extreme. Sorry.