You can download the Silverlight 3 and RIA Services tools here but be aware that they cannot be installed along with Silverlight 2 tools! If you do not have a separate test environment to install into you can still install Blend 3 (which now includes a code editor) next to your existing Silverlight 2 environment to work with SL 3 projects.
Completed demo code: CohoRIA.zip
Thanks to Rob Bagby, who created the demo application. He has the Coho Winery database used for the application available from his blog. Look for the link on the lower right.
Be sure to check out Brad Abrams’ original session from MIX.