Is it legal to make and sell a new program (client) that uses with
another company's server as an alternative to using the other
company's own program? This is assuming that the protocol is not
officially "patented" and the research is done by observing the data
sent/received through the network. Specifically I am concerned about
USA laws (and Canadian laws although that is secondary).

I am aware of programs like Trillian, but I believe they are usually
not from USA/Canada... so I am looking more for general information
than any particular program (I'm just using Trillian as example so its
understood what I mean by new client program).

Looking for CREDIBLE sources where the source/speaker is not an
anonymous person. Newsgroup and forum posts are specifically NOT
desired.

PS: Yes I am aware of the policies of not relying soley on Google
Answers for final legal advice, blah blah.