Actually you can use the MT-24EX as a master and the 580EXII as a slave. It's a little unreliable in direct/bright sunlight, and they need to be in direct line of sight with each other. Not really practical, though, for portrait.
I'd suggest you investigate thoroughly before buying Pocket Wizards. They are the "gold standard", but there are quite a few cheaper alternatives that would be more than adequate for your purposes. As always, I'll point you to the flash/lighting section of POTN and also refer you to strobist.com
Predicatable, aren't I.