BackupBuddy Minimum Requirements

Unix. This is developed on RH Linux (Red Hat ES, Fedora Core 1).
PHP 4 as a CGI or CLI module. (EG: /usr/bin/php) Untested with PHP 5, but reported working.
ssh configured so that login from the backup server to the backed up system happens without a login prompt. See this page for a quick howto.
rsync 2.5.7 or later. (with support for --link-dest option)