clustering: how to start?

[Koza Zbigniew]

We have just bought 4 dual-processor Xeon boxes for a physics
department and want to turn it into a computing cluster.
This means we want that the users will communicate with it via
ssh/sftp and see all processors as if they were part of a one virtual
UNIX machine with 8 processors on board.
A typical job we want to run is
(a bunch of) numerical simulation programs that run for 2 weeks or so.
Thus, the cluster will serve only as a numerical workstation.

We have experimented with Debian and OpenMosix. The first outcome of our
tests is that Intels' so much advertised Hyperthreading technology is a
disaster. Then, OpenMosix seems to have a bug that can bring the whole
system to halt if one tries to run simultanieously several
memory-consuming processes.
We have also problems with compiling custom Linux kernel so that it
could see all the swap space and memory it should see.

Then I recalled that several years ago I experimented with FreeBSD and I
liked it. Now I hear that FreeBSD supports SMP "natively", so
no kernel recompilation will be necessary.
I thought - maybe we could try and use FreeBSD instead of Debian?
Now my question is: where should I start?
Which docs should I read?
Which program(s) should I use to cluster our 4 FreeBSD boxes?

regards,
Z. Koza