<?php
function copyrightDate() {
	global $wpdb;
	$copyright_dates = $wpdb->get_results("
		SELECT 
			YEAR(min(post_date_gmt)) AS firstdate, 
			YEAR(max(post_date_gmt)) AS lastdate 
		FROM 
			$wpdb->posts
	");
	if($copyright_dates) {
		$copyright = "Copyright &copy; " . $copyright_dates[0]->firstdate;
		if($copyright_dates[0]->firstdate != $copyright_dates[0]->lastdate) {
			$copyright .= '-' . $copyright_dates[0]->lastdate;
		}
		echo $copyright . "&nbsp;" . get_bloginfo('name');
	}
}

?>