If you have under 100 pages Google will crawl your site naturally (if you have a decent backlink) way faster than it will your sitemap. If you have deep pages or perhaps java or flash links then I would recommend getting one. On the other hand, it's pretty easy to make a sitemap so why not?
One more thing. If you're talking about a regular sitemap then yes, you should have one for the crawlers. It's the XML I was talking about
Yeah. Sitemaps are needed to let the googlebot know that your site has been updated and has to be crawled again. It is worth the time spent in creating one (There are free tools available to create them and the time required is minimum so that you can create one right now!)
Having a sitemap almost (not always though...) guarantees getting indexed in Google. Yes, you should create one, just search for "sitemap creator" in Google.
I'm using XSitePro and XSP publishes a sitemap automatically. I'm very happy with that, because new pages are indexed (in my opinion) faster thatn they would be without sitemap.