Joomla CMS requires mod_rewrite. This can be a problem when using shared webhosting where SAFE_MODE is in effect.
Joomla uses mod_rewrite and .htaccess files. In global Apache conf you need to set something like:
<Directory "/path_to_your_vhost/www.your_domain.com/htdocs"> Options Indexes FollowSymLinks SymLinksIfOwnerMatch AllowOverride All </Directory>
SymLinkIfOwnerMatch allows to create symbolic links only to those files whose owner is the owner of the symbolic link.