I hit a weird error when trying install the Orcas Beta 1 on Vista today.  After some searching, I found this entry from Aaron Stebner with a simple fix.  It turns out that there's a bug in the .NET 3.5 installer.  If your installation path includes spaces, it will fail.  The error isn't at all clear, and certainly spaces should be fine, but a lack of quotes in the installer script causes the failure.  Simple fix, but it sure wouldn't have been easy to find!  Thanks Aaron!

I am very pumped about Orcas.  If this ever finishes installing it will be awesome!