I've just uploaded a new version of TestDriven.Net with support for Silverlight 2.0 Beta 1. Microsoft have certainly kept me on my toes as there have been lots of changes since Silverlight 1.1. I'm sorry it has taken a while!
At the moment you're limited to running individual public methods (ad-hoc tests). If you need to run a suite of tests I recommend you use this in conjunction with the Silverlight Testing Framework that was released at MIX. Jeff Wilcox has posted a detailed tutorial that shows how to use the framework here. When running your tests using 'Test With > Silverlight', bear in mind that you're simply executing the test method and any test attributes (TestInitialize etc.) will be ignored.
I've also included an application called 'agx.exe' that lets you run console applications using the Silverlight/CoreCLR from the command line. After you've installed TestDriven.Net you will find this standalone application here: \Program Files\TestDriven.NET 2.0\agx.exe. This is simply an application that I use for my own testing purposes that I thought other people might find useful.
You can download the new version of TestDriven.Net from here.