Where? At Tor.com! The audio clips are taken from the first chapter — Amber’s first, then Wil’s (they’re reading sequential bits, not the same bit).
I’ve listened to them. I am sooooo happy with these audio versions, I can’t even tell you. Except, uh, I just did, I guess. Anyway.
Also, remember that for the next four days (through the 22nd) if you pre-order one version of the audio, either by Wil or Amber, you can get the other one as well. Details are here.