Ethernet library help

Can anyone suggest a good reference for learning how to efficiently use the Ethernet library? I have successfully modified the examples to do useful things but I don't really understand enough to write an application from scratch.

I am writing an e-mail client and so far I am getting the correct response strings from my server but as I implied, I don't feel comfortable with the parts of my program that I have just copied from the examples.

The Wiznet 5100 factory documentation is sparse at best or perhaps I haven't found the proper literature yet. Any suggestions about that would be appreciated.

I'm literate enough to follow any textbook on the subject if someone can suggest one.