@mx150: Go to Help/System Info to find out which PHP version you are actually using. More than once, people thought they were running 5, but it was really 4.
@Nancy: No, PHP is required. As far as being dangerous, PHP4 is dangerous, since it hasn't been updated in quite some time, including security risks. As stated in the download, PHP5 is required... and PHP4 is never recommended, with or without CB.