The jury is still out on whether submitting a sitemap to Google makes a spit of difference to your rankings or not, but it would still appear that it does no harm. The problem has always been that downloading the Google software to generate a XML sitemap is a bit of a tech nightmare, and definately out of reach of most folk.
I've found a great website that will quickly spider your site and generate a XML sitemap to Google's specifications. Just pop in your URL, wait a bit then copy the generated sitemap and copy it into notepad, then save it as sitemap.xml and upload it to your website. From there you just need to know the URL of your sitemap through thier webmaster tools site.
Easily generate your XML SiteMap here - http://www.xml-sitemaps.com/