I have developed a tool called MidiTangle to send midi over a local network. This is a program that I use and am making available for free to others. Please give it a try, those who might find it useful. I have a two computer setup in my project studio with synths/sampler on one and Sonar on the other.
Note -- MidiTangle requires a midi virtual port driver like MidiYoke or MapleMidi. MidiTangle sends and receives midi over a network peer-to-peer. It takes midi from a port, sends it over the network, and on the receiving computer sends it out to a midi port. My setup is W2k. It should work on any MS OS W2k and up provided a working midi virtual port driver is available.