as Cranky said it is not supported, besides that you will run into dependency errors with rpm 4.3 (Plesk expects 4.2). After you have solved that you will find mysql 4.1.7 as a potential problem. And I think you might also get problems with the SELinux implementation.
We are still waiting for a Fedora Core 3 release, FC3 has the RHEL4 features but is also still unreleased.
We might be lucky if Plesk 8.x will support both distributions.