Audun,
I think he meant he is using Giga on the same box as his sequencer is running on, alongside two other computer that each have an instance of GigaStudio running, which is a "total" of 3 GigaStudios on 3 computers. The composing is done with the sequencer, and later on he has to mixdown to one file from the different GigaStudio's.
You can use 3 computer screens each connected to one computer, but I doubt this would be a useful setup, unless you got the space for it (keep in mind, this also needs additional keyboards and mouse, and what if you want to expand?) - For some a better solution is using a KVM Switch (keyboard vga mouse switch) which allows you to access three computers by pressing a key for each, while using only 1 keyboard, 1 mouse and 1 screen. Another way is to do the same with remote software that is running via network device. That way you can remote control the other computers, it's cheaper, but not as fast as the hardware way with the KVM Switch.
Today there are graphic cards to support 3 screens at once utilizing only one computer, think of Matrox Parhelia, but it's not too common yet. The only case this would make sense in such a setup is, if you want to have your sequencer spreaded over three screens. DualHead graphic cards (such as the Matrix G550) are sufficient for most (and cheaper), having the sequencer displayed on two screens. The seperate GigaStudio computers not necessarily need to be displayed by the computer running the sequencer.
Hope this helps,
PolarBear