If you have different versions of PostgreSQL database servers you need a pgadmin III version with the respective pg_dump and pg_restore included.
I am running pgadmin III on a windows machine.
For example for PostgreSQL server 8.4.x you need pgadmin III with pg_dump 8.4.x, for PostgreSQL server 8.3.x you need pgadmin III with pg_dump 8.3.x and so on.
What I cannot figure out is how do you know which version of pgadmin III contains which version of pg_dump and pg_restore? I could not find the info on http://www.pgadmin.org/download/windows.php
I could just install some versions and try out, but maybe there is a better way.
pgadmin III V 1.8.4 comes with pg_dump 8.3.15