Theoretically, in Erlang, writing a parallel program for many computers is not much different from writing a program for a single computer. Each process on each processor has a unique id/name. Processes can be easily spawned. Messages can be easily sent and received. Each home directory on each computer will have a special Erlang cookie password file that allows access to Erlang processes on that machine.
The major problems people have writing distributed programs in Erlang are general network reachability issues related to firewalls and routers.