Taken from Rod Trent's Blog...
Thanks to Paul Thomsen at Microsoft for posting these to the SMS email discussion list!
Main presentation – you have to sign in but that then leads to the live presentation, or the PowerPoint slides (or it should – it’s busted now), or the offline viewing download
WMA – voice-over only (podcast, I suppose you could say)
MP3 – same thing but for devices that don’t support WMA
PowerPoint slidedeck direct download - you don’t have to sign in