Microsoft’s Press Article:
http://www.microsoft.com/presspass/press/2007/sep07/09-04SilverlightPR.mspx

Here is a great place to start, if you are interested in Silverlight
development: http://www.silverlight.net. The runtime, and SDK can be
downloaded at: http://silverlight.net/GetStarted/.

In the coming weeks, I expect we will see lots of comparisons between
Silverlight at Flash.

Quick Summary:
(I expect most of the comparisons will boil down to)
* Silverlight is heavily focused on great video
* Silverlight with CLR/.NET will be easier for existing .NET developers
* Flash users will probably not switch (unless dealing primarily with
Video).
* The competition will be good, and should drive both products to improve
support/functionality for Rich Internet Application development.