understanding 9grid and clustering?

hi!

i have some beginner's questions about 9grid and clustering.
i have plan9 installed only on single computer at home, without any 
network interface
so i have never tried cpu command :-(

questions:
1) is 9grid only a group  of  cpu-servers and anyone can decide where to 
run cpu command?
2) can parallel program run on more computers at same moment?
3) can forks or threads run on different machines?

thanx everyone for answering my (maybe stupid) questions.

alexandr babic.