JavaScript vs C# for client side

I thought that you may have this in mind! I think that the most important thing that can't be done using server code is to alter the page content without refreshing the page. And if we go further, with client code you can do virtually anything with the viewable area of the browser. I have seen a real 3D action written in javacript.

I guess what I was getting at in my poorly formed question, is there anything that can't be replicated using server side code that is traditionally done with javascript? (i.e. field validation, etc).

C# on the client side?! I haven't heard before that c# code can be interpreted on the client side. Which browsers support this? Does the client has to have the .net framework installed?