Problems with Scyld and mpirun

[Pat]

I'm an undergrad and have been working on getting a simple 5 node
cluster (of Pentiums) up and running for some simple parallel computing
experiments. I've gotten Scyld ("Label Side Up Edition" ver 27bz-8) up
and running fine. However the problem I'm having is that I can't get
mpirun to work correctly. Using linpack and the mpich example programs
included in /usr/share/mpich/examples/ I can only get the processes
running on the head node.

-The four children nodes all respond "up" in beostatus.
-I've installed pvfs according to
http://www.cs.concordia.ca/Beowulf/pvfs1.5.1/pvfs-scyld-howto.ps
-I've tried every variation of the mpirun command I can think of.Setting
the env. var np=4, using the -nolocal flag, and creating a
machines.LINUX file.
-I can use the BProc system calls to pass messages and compute on the
child nodes, however I want to write somewhat cross-platform code.

I feel like I need to install some library or rpm that the default
install fails to. However I've looked high and low and none of the
install tutorials mention any extra steps beyond the default install.

Thanks for the help,
-Pat