Hello and welcome to X10,
Yes you can use silverlight, But beware since most users on the internet haven't bothered with downloading the siverlight addon.
Hey, Silverlight is very easy to install as an addon and can be served from an apache server.. You might not want to do any streaming video though since it will eat your bandwidth and may be cause to get you suspended for high resource usage. The other thing is to try and stick to the silverlight .net libraries as any other assemblies will have to be loaded with it... I probably don't have to mention streaming video probably isn't the best idea.