Submitting sites to search engines is a waste of time and totally unnecessary.
The best way to get Yahoo, MSN or Google to index your site is to obtain a link from a page that is already being indexed by them.
Links from other sites to yours are extremely important and you can read about them here http://www.seo-blog.com/inbound-links.php and here http://www.seo-blog.com/directory-links.php