Hehe was researching on Google and stumbled upon my own thread
Update jan 2013 - my 2 DAW computers together (my quad core & older single core machines) connected via their own sound cards, just using 5-pin midi from master into slave, running some VSTi's, sending it's analog audio from slave to master. This worked so well as a VSTi machine (like any other outboard midi device) , that I decided to build another far more capable quad machine (a replica) to replace my old single core machine being it couldn't run as many VSTi's as I'd like.
I had tried experimenting using my ADAT connections between the computers via the Aark 24 cards, but couldn't get it to work for some reason. I'll try again at some point, along with experimenting with other methods that have been discussed in this thread. Using old standard midi and analog audio is fairly straight forward, though there are benefits between various methods of course.