I've managed to get a few games in with GB folks and I highly recommend anyone new just jump into the giantbomb chat channel in DOTA. There will almost certainly be someone pretty much any time of day that will help you out.
@zgoon: I've just been playing Normal and it's been going OK - it only gives you three heroes to choose from and generally everyone else in the queue is similar skill to me.
I've also found that Purge's videos (https://www.youtube.com/user/PurgeGamers) are helpful, though they are pretty long. Really just playing is probably the best way to go, though I think just jumping in to play against real people is the best way to learn.