If you go through Microsoft's Download page for the Service Pack 1 Beta for Windows 7 and Windows Server 2008 R2, you're going to have to jump through some hoops to get it. In fact, you might even have to lie: If you inform Microsoft that you're not a developer, the site will inform you that this release is only for developers!
That's silly.
So in the interest of not making a liar out of anyone, here are the direct download links.
Standalone update (ISO format, 1.2 GB)
64-bit (x64) Edition using Windows Update
32-bit (x86) Edition using Windows Update
Note that the download(s) may be more efficient if you go through the normal channels, as Microsoft provides a download manager.
UPDATE: Ah, crud. They're on to me. :) These links aren't working. I tested them on different browsers on one PC, but when I test on a different PC, no go. I'll try to figure this out ....
UPDATE: These links will work properly if you copy the URLs (right-click, Copy Shortcut) and then paste them into the Internet Explorer 8 address bar. This installs and then launches the download manager and appears to work whether you're logged in with a Windows Live ID or not.