Try this:
function PluginUrl() {
//Try to use WP API if possible, introduced in WP 2.6
if (function_exists('plugins_url')) return trailingslashit(plugins_url(basename(dirname(__FILE__))));
//Try to find manually... can't work if wp-content was renamed or is redirected
$path = dirname(__FILE__);
$path = str_replace("\\","/",$path);
$path = trailingslashit(get_bloginfo('wpurl')) . trailingslashit(substr($path,strpos($path,"wp-content/")));
return $path;
}
echo PluginUrl(); will return the current plugin url.