It seems that you are using the first release of the Composite Application Guidance for WPF, which only targeted the Windows Presentation Foundation.
The P&P team is currently developing a new version of this guidance which also targets
Silverlight. This guidance named “Composite Application Guidance for WPF & Silverlight” (or Prism-v2) should help you create a composite application using Silverlight. The latest drop can be found
here. The documentation from the drop should help you get started
in the usage of this guidance.
In addition, both for this and the previous version GAT and GAX are not required.
Please let me know if this helps.