Currently the HTTP servers over at Apple Dev are overloaded however going in over HTTPS is fine.
Change the http:// at the beginning to https:// and the pages will load and provided you have an Apple Developer Membership you can d/l the SDK / Beta :)
so…. https://developer.apple.com/iphone/
Chris
update: this is now going a little slowly too!
update: ‘humbertog’ just posted on Twitter: “By installing iPhone 3.0 beta on your Test Devices, these devices are permanently “locked” into testing mode and cannot be restored!”
Does anyone know if this is true?!

humbertog is correct, he is quoting the preinstall release notes that you should have read. Apparently the only way to go back is to put your phone into DFU mode and then restore. I haven’t yet read about someone attempting this yet and what their outcome was.
I also understand that MMS does not yet work.
Oh okay, so anyone with any Jailbreaking experience should be fine :). I’ve taken a read of the docs now… learnt my lesson :).
MMS.. really? That’s rubbish; it was listed as a feature!?