Windows Vista beta 2 is now available for download. Get it now!
You need to use a download manager, or at least a browser that supports resuming downloads, since it is a gigantic download, or you can use Microsoft’s provided manager from Akamai. You should expect 3.2 gigabyte download (4.4 GB for 64-bit), so free up some space. Do not bother downloading unless you can burn it to a DVD. You can also order a DVD, and pay for shipping.
You need to free up 11.23 gigabytes before attempting installation. No, that is not a typo. Vista installation will refuse to upgrade your machine with even one megabyte less, and will insist on a clean install. Be prepared to move some stuff to other hard drives.
Vista Beta 2 expires on July 1, 2007.
There is a more detailed download page here.