If you want to save a site collection as a site template you can go to site settings and select "Save site as template" from the Site Actions section.  However, if you go to site settings from a subsite, the option doesn't exist.  Is all hope lost?!  Not at all!  Just append "/_layouts/savetmpl.aspx" to the site URL.  So, if you want to create a site template from http://myportal/mysubsite, enter http://myportal/mysubsite/_layouts/savetmpl.aspx into your browser's address bar and you'll get the site export page.