Rob, ipMIDI sounds interesting. Do I need to install it on both machines or just one? If I install it on the Mac, how does the PC find it? If I open Sonar Home Studio, will there be a port in there that says "Ethernet MIDI" or something like that? Their website doesn't really explain that much.
You would install the Mac version of the program on the Mac and the PC version on the PC.
Follow the instructions on the installation process and you should be ok. (This is my way of saying, "I don't remember what I exactly did to get it to work - but it was very easy and I didn't have any trouble with it.)
And yes, once you install it, ipMIDI will show up as a MIDI driver in your programs.