Preserving profiles during an upgrade FC3->FC4

[Paul Michael Reilly]

I would like to do a fresh install of FC4 to a server running FC3.
About the only thing I care to preserve is the User profiles.  I
suspect it is a little more complicated than just migrating
/etc/passwd and /etc/shadow.  Can anyone point me to a howto?

This server goes back to Redhat 9, possibly earlier.  I've been doing
in-place upgrades every six months or so.  There is so much cruft
lying around that it is high time to bite the bullet and do the clean
install.

Thanks,

-pmr