Due to excessive demand of Windows 7 Beta from Windows enthusiasts around the world, Microsoft servers have crashed under heavy load as also reported on the official Windows Team Blog:
Due to very heavy traffic we’re seeing as a result of interest in the Windows 7 Beta, we are adding some additional infrastructure support to the Microsoft.com properties before we post the public beta. We want to ensure customers have the best possible experience when downloading the beta, and I’ll be posting here again soon once the beta goes live. Stay tuned! We are excited that you are excited!
Fortunately, The official direct download links for both the x86 and x64 version of Windows 7 are still up. You can go and download it right now without having to wait for Microsoft to put them back again through their Windows 7 Customer Preview program. The Beta bits of Windows 7 are set to expire on 1st August, 2009.