There is a quick Getting Started with Silverlight page here, but I thought I would extend this a bit with my own experiences.
First, I highly recommend going the route of using the VPC Images for Orcas because you can easily hose up your development PC so that when Orcas is released things will never be right! However, you'll need some chubby disk space for the VPC image - about 15 GB.
So here is the order of downloads:
1. Orcas Beta 1 VPC (first download the Base Image and then all of the .rar files containing the differencing images)
2. You will also need to install the Silverlight 1.1 Alpha runtime on the VPC image.
3. Next you can install the Silverlight Tools Alpha for Orcas.
4. If you made it this far, you can now start with the QuickStart Tutorials for 1.1 Alpha.
It appears there is no XAML designer yet for the Silverlight Alpha template inside Orcas (not even a bad designer) but you can copy-and-paste XAML from a WPF application template to get by.