Now I have, and thank you for this info. However I have been waiting over two months and google did not index my pages in webmasters tools. My sitemap is genereted automaticly in Joomla by 'JM sitemap' therefore since <changefreq> is set to yearly I was wondering if this is causing the problem...
A sitemap ideally should be in xml format and not html format. There are many free sitemap validators that you can use to identify check your sitemap and identify any errors in it.
I suggest you carefully read the info at sitemaps.org. That is the official sitemap protocol that the major search engines follow.
As for crawling frequency, the search engines use that as a suggestion and do not strictly follow it. If they strictly followed it, people would abuse it and simply set every page change frequency to "always". If you set a page to "yearly" it will likely be seen as a lower priority to the bots.