URL rewriting can bring you on the right track in the race for SEO combined with other techniques that you may use for this purpose. But be aware that rewrittenand, presumably, better looking and more effective in terms of search engine ranking URLs cannot substitute a poorly designed Web site. For example a URL that contains "seo_techniques" will be shown by the search engine only if the user searches for seo_techniques whereas searches for "seo", "techniques", or "seo techniques" give your "seo-techniques" containing URL a better chance of being displayed on the SERPs.