No IronRuby install is required to develop and deploy Ruby applications for the browser, though you can always download the pieces hosted online (for working without a network connection).
IronRuby in Silverlight re-distributable package
Zip-compressed file containing all the pieces needed to develop and deploy Ruby applications for the browser. Here are its contents:
Handles enabling the HTML page to run Ruby code with IronPython in Silverlight.
Actual static Silverlight application, which has logic for executing Ruby.
Microsoft.Scripting.slvx and IronRuby.slvx
IronRuby binaries, including the Dynamic Language Runtime.