Already is an adverb. It means either (1) by a specified time, or (2) so soon. The two-word phrase all ready means completely prepared, or it’s used to indicate that everyone in a group is prepared.
Examples
In these cases, already is appropriate because it is an adverb:
Doesn’t nearly everybody already have a TV (or several) at home? [Time]
Britain has already begun to slide back into recession . . . [Telegraph]
Her gorgeous, antique-inspired hair comb is already available for purchase at Hot Topic. [MSNBC]
And these writers use the phrase all ready well:
For most, it was their first feature, and they were all ready to be guided by their confident director. [Guardian]
I’m all ready to shop online this holiday season, but I like to save a little when I can. [USA Today]
And Darpa’s got a nifty new computer program on their hands, all ready to roll. [Wired]