No not really. The messages from Joomla are really warnings, not errors and are due to the setting for magic_quotes_gpc in the php.ini used by the default DreamHost PHP5 install. Joomla should still function fine, despite the warnings and, as I understand it, the security issues are not too severe.
If the warnings do concern you, you can change the magic_quotes_gpc setting for PHP5, but this involves copying the default DreamHost PHP executable and php.ini files to your domain, configuring your .htaccess file to use this local install then modifying the required php.ini settings. The general procedure is detailed in the wiki article linked below, but I should warn you that the procedure does require a fairly good working knowledge of the shell etc.
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