.NET Framework 3.5 Beta2 is available for download from MSDN.  You can acquire it by going to the following link:

http://www.microsoft.com/downloads/details.aspx?familyid=d2f74873-c796-4e60-91c8-f0ef809b09ee&displaylang=en

Additionally, Daniel Moth has a good post describing .NET Framework 3.5... I though i'd share part of it here as it is likely better than one I could do... thanks Daniel.

For help with troubleshooting the installation please post on the .NET Framework Setup Forum.