In a new note from DynamicWebPages today, there's an announcement of the posting of PHP 5.1.0RC5 over on Ilia's download site.

Ilia Alshanetsky, release manager of the coming version 5.1, released today the fifth Release Candidate in the 5.1 series. In the last RC there were still some errors that were found, but they should be repaired with this RC. Like always you all are called for testing.

You can download this latest release candidate from Ilia's downloads.php.net site...