goodroi - 12:16 pm on Nov 16, 2009 (gmt 0)

Technically you don't need to resubmit the sitemap. Technically you don't even need to use a sitemap. Search engines use many ways to discover your content. They prefer to discover new content by following links, they also use RSS feeds and toolbar data. If your content will not be discovered through those ways then you should think about using a sitemap.

I don't know all the details of your personal situation but I would speculate that it could be a good idea if you updated your sitemap every 1-2 weeks.

You could try a simple experiment. Don't update the sitemap and see if the content is indexed. That will let you know if you really need the sitemap or not.