If, as you recommend, no one is using the "main computer" in a peer-to-peer network, is there any reason why a server-client network would be faster or more reliable?
Well, besides the fact that a real server with a real server OS will always be faster and more reliable, than the alternative, yes it would be more reliable.
The real problem with your question is I don't understand it.

Can you please clarify. By definition (to some extent), in a client/server setup, no one is using the server, so it is MUCH more reliable and safer.
--Excellent point on Paul Thurotte's methodology and WIN7. One would have to think Microsoft would catch on.