Sure, it isn't a 30 day demo, but these iLife '08 tutorials give you a very nice overview of what the various apps can and can't do (and how they do and don't do 'em). The short videos are very task oriented, as you would expect with tutorials, and best of all they are free.
Check them out, and see what iLife '08 has to offer.
Oh, and can someone explain to me why I need to go to a store and buy physical CD's to get iLife? Apple is one of the world's largest distributors of digital music, and I am pretty sure they can handle digital distribution of software as well. Ah, another mystery of the universe.