Microsoft seems to be up and down with the Windows 7 beta 1 download from the Windows 7 homepage.
This worked for me:
Get a Live account (hotmail, whatever)
Go to http://technet.microsoft.com/en-us/default.aspx and login on the upper right (you may have to create a profile)
Paste this URL in to the browser to get either ISO:
Windows 7 Beta 1 32Bit (x86) or Windows 7 Beta 1 64Bit (x64)
Now the tricky part, Get a key to activate and install the beta:
(I had a lot more luck using Internet Explorer than Firefox)
That's for a 64bit product key, product keys between 64bit & 32bit are interchangeable.
Make sure you're still logged in to technet (upper right of the screen), You may have to refresh a couple million times. If this is taking you forever don't forget to check back at the Windows 7 homepage for updates. This is a workaround solution because Microsoft keeps pulling the Windows 7 beta links off of their Windows 7 page.
Good lucky & happy refreshing.