Krisw,
Thanks for the post, and welcome to the Netduino community!
Speaking of which...would you be willing to share your code for the W5100 shield with the community?
We're working on a few Ethernet options as well... As far as integrating W5100 into the .NET MF, that can be done either in managed code (by creating a replacement for the System.Net classes) or in native code (by writing a "native driver" for the shield).
Chris
Sure, although I will admit the code is fudged out of various bits of other peoples efforts on the net. I need to tidy it up and check it all works without blowing up!
Is there a default place that all drivers get deposited?