Difference between wheat and barley?

[strangecarr]

Can anyone tell me what the actual difference between wheat and barley is?
e.g. different characteristics, different fermentables etc...

Also, what other malt can be used for brewing - rye?

 

[brewitnow]

John Palmer gives a nice run-down:
http://www.howtobrew.com/section2/chapter12-1.html