A couple things... you we're mentioning clients including linux. If your
looking for interopability with non-MS clients you may want to investigate
web services. They're ideal for connecting together systems that normally
can't "talk" to each other easily.

As for your firewall question. A firewall basically blocks/allows connection
to certain ports. To allow your application to be firewall friendly you'll
have to open up the port that your .net remoting component is on your
firewall to allow outside connections to hit your "inside" server. If you
we're to do this make sure you take additional security procautions as
needed. The reason that http is is usually firewall friendly is because a
lot of time port 80 is open on firewalls to allow internet access.

As for your Kazaa comment I think what you might be referring to is a proxy
setting that allows all the internet access on your local network to funnel
through a single server that provides your internet connection.  There is no
"work through firewall" setting because opening ports is solely configured
in the firewall and it would defeat the purpose of a firewall if clients
could just say "Ignore the firewall" :)

Hope this helps.

Regards,

Josh Carlisle