To find out what internal links that Google has indexed go to your Dashboard and look under "Your site on the web/Internal links".
A good indication of your "presence" on the web is to look at the "Links to your site" section". To find out which sites are linking to yours, click the "Find" button for the URL - http://www.website.com/. Add - AnyPageName.html - into the box to find external links to a specific page.
Its interesting to to look at these links to see which ones are "quality" ones - those that come from other sites with a large amount of traffic. For example, iWeb for Musicians has about 600 incoming links but only 20 or so coming from well established websites. This tells me that I should start taking advantage of all these link exchanges that I am being offered! When you realize the importance of these external links you will see why it is essential to use keywords in your domain name, sub site and page names. In other words, page names like Welcome, About, Contact etc are useless.
To increase the effectiveness if keywords in page names its apparently more effective to separate the words with hyphens and NOT the underscores that we see so often.
Thanks to everyone for their ideas and suggestions. My site map is still only producing one indexed URL but, more importantly, Google is now finding all my pages! Not sure what solved the problem - whether it was removing that weird metatag I'd put in my URL, or resubmitting the sitemap, or verifying again with the HTML file, or something else entirely. But I am now where I wanted to be when I posted the question, so thanks again to all.