I have GPO on 2 PC machines as you get 2 authorizations.
My machines are networked together with FXTeleport. This allows MIDI to go over the network with no need for MIDI interface and cables. The digital audio comes back over the network interface so you don't need an audio card on the 2nd message. There is a little bit more latency when recording but playback is always right on.
I use Sonar as my sequencer on my main machine. This loads the VST's on both machines and saves all the data on my main machine. When you load the song in Sonar it loads the song and all the VST's on both machines including GPO, Kontakt, VST effects, etc.
I use Remote Desktop Connection on my main Windows XP machine to load the sounds in Kontakt on the remote machine which is located on the other side of my house.