a pc and a mac, both networked so files can be transferred from one to the other, just wish i could send midi down the same wire ... use the net mostly on the pc and do most sequencing on the mac.
There is a program called midi over lan, never used it before and have no idea if it works for mac.
There is also FXteleport which enables you use vst instruments and effects over a lan as if they are on the host machine. Once again not used it yet, but i will do once my lan is setup.