iOS installing applications (specifically iphone 3.0 beta/sdk)

Hey there. I just got my first mac, and I'm still having trouble catching onto the installation process for these things.

I downloaded the 3.0 software for the iphone (I'm finally going to put my years of programming classes into affect to develop apps), but I have no idea how to get the SDK running (do I just start xcode?) or how to get the 3.0 beta onto my iphone.

Any help would be appreciated!!

Thanks!