RSS Widget (sidebar) coding?

I’d like to re-format how RSS feeds are displayed in my sidebar. I’ve added an entry to my functions.php but am having a heck of a time finding the code to generate the RSS feeds in the sidebar. Does anyone know where I can find this?

I tried looking in the widgets.php file in wp-includes, but when I plopped that code into my widget_mytheme_rss() function, the result is the pre-programmed error message: “An error has occurred; the feed is probably down. Try again later.”

Code snippet:

function widget_mytheme_rss() {
	//$title ? print($before_title . $title . $after_title) : null;

	if ( is_array( $rss->items ) && !empty( $rss->items ) ) {
		$rss->items = array_slice($rss->items, 0, $num_items);
		echo '<ul>';
		foreach ($rss->items as $item ) {
			while ( strstr($item['link'], 'http') != $item['link'] )
				$item['link'] = substr($item['link'], 1);
			$link = clean_url(strip_tags($item['link']));
			$title = attribute_escape(strip_tags($item['title']));
			if ( empty($title) )
				$title = __('Untitled');
			$desc = '';
			if ( $show_summary ) {
				$summary = '<div class="rssSummary">' . $item['description'] . '</div>';
			} else {
				if ( isset( $item['description'] ) && is_string( $item['description'] ) )
					$desc = str_replace(array("\n", "\r"), ' ', attribute_escape(strip_tags(html_entity_decode($item['description'], ENT_QUOTES))));
				$summary = '';
			}
			echo "<li><a class='rsswidget' href='$link' title='$desc'>$title</a>$summary</li>";
		}
		echo '</ul>';
	} else {
		echo '<ul><li>' . __( 'An error has occurred; the feed is probably down. Try again later.' ) . '</li></ul>';
	}
} 

if ( function_exists('register_sidebar_widget') )
	register_sidebar_widget(__('Links'), 'widget_mytheme_links');
?>

Any help/ideas, or a general nudge in the right direction would be VERY helpful. Thanks!