Pruebe con:
Código PHP:
<?
echo "<a rel=\"lightbox[roadtrip]\" href=\"".get_post_meta($post->ID, '1', true)."\" rel=\"bookmark\"><img style=\"float:left;margin:0px 8px 10px 0px;\" src=\"".get_post_meta($post->ID, "1", true)."\" alt=\"".get_post_meta($post->ID.'Theme Name', true)." Imagen \" width=\"158\" height=\"120\" /></a>";
?>