There’s been some confusion with setting up Silverlight development the VS 2010 Beta 1 release, since the Silverlight SDK and developer runtime are part of the installation. In order for Silverlight to work in VS2010, you need to install both the SDK and developer runtime, but there is not a separate package for the Silverlight Tools itself. This will be fixed in the next beta of VS2010.
For now, if you want to install these packages, here’s some links:
Note that there are some issues when using Dev10 Beta 1 with Silverlight 3 RTW, but most of these can be worked around. We’ll have more info on that soon.