We just went through the update process for PHP and MySQL on RHEL4 with Plesk 8.1 originally installed, and I wanted to give props to the ART folks for making their RPMs available. Hopefully sharing our experience and a guide to avoiding all the "gotchas" we encountered along the way will give a little back by being useful to a few people, so here it is:
RHEL4 + PLesk 8.1 Upgrade Notes