Even if you could make this work the browser would have to support it on the
client and that would mean, at a minimum, the .NET runtime would have to be
installed on the client and probably the browser would have to be IE6 as
well. Unless 100% of your users are a captive audience under your control,
e.g., an intranet or a very tiny group of users where you can dictate the
appropriate client requirements, then you'd be sunk.
All modern browsers support JavaScript, that is why it always gets used on
the client. That is also why VBScript was never widely used on the client
side even though IE easily supports it. Even when you can get away with a
different language in certain circumstances, for broader code reuse you want
to stick with something that will work anywhere and where browser vendors
will feel obligated to support it. I can't imagine FireFox supporting C#
for example, since it's a product of the Evil Empire.
--Bob