The poster for Silverlight mentions support for VB.net and a language called VBx.

VBx stands for VB10 as it turns out, and it will become a dynamic language that you can script with and will run anywhere that the new Dynamic Language Runtime will run, say on a Mac as well as Windows. The bad news (which is predictable these days) is that it’s not in the Silverlight 1.1 alpha, and is planned to be in a Visual Studio release after Orcas, so it’s ‘just’ VB.NET and C# support for 1.1, although there may be the new .NET DLR-integrated/interoperable versions of JavaScript, IronRuby and IronPython in there. In Silverlight, all these languages act as the control logic for WPF-subset UI.

Get the the more official details.

Check out this Mix07 session that includes a demo of VBx from about 21:30, building using a text editor on a Mac.