When you log in to the master node, your account is already setup to use MPICH2 as the default MPI implementation.
When you log in to the master node, you will find a directory named pvm3 in your home directory. This directory is setup (when you login for the first time) for PVM to work correctly. This directory contains a sub-directory bin, which contains a sub-directory named LINUXI386, where LINUXI386 is the architecture of the system as used by the PVM system. Your PVM executables normally reside in the ~/pvm3/bin/LINUXI386 directory, which is already set to be in your PATH.