As mentioned by the International PHP Magazine site and on this Trac page for the Roadsend SiteManager software, they're working on porting it up to PHP5.

The latest available version, Roadsend PHP SiteManager 4.0.0 beta, was ported to PHP5. Database access has switched from PEAR to PDO. A script is included to help port existing projects. This version of SiteManager no longer uses PEAR DB - it uses the PDO database routines in PHP5 so there are a few changes to make. There is a script included in bin/php4tophp5.php which you can run on your current scripts to make most of the changes

Currently, you can download the latest beta from their website and check out the Trac website for the project to keep up with the latest advancements.