Reply #4: You want a Content Management System

[salvorhardin]

I always recommend Drupal and now that it has integration with Gallery 2 it seems perfect for what you're describing, which is rather vague. One word of advice: wait until Drupal 4.7 is released. There are many changes and improvements between 4.6 and 4.7. Drupal 4.7 Beta 2 was just released so the production release of Drupal 4.7 shouldn't be more than a few weeks away. Both Drupal and Gallery are free.
http://www.drupal.org
http://gallery.menalto.com

As far as learning PHP and XHTML (don't bother starting with HTML - XHTML is nearly the same) this is a good idea. Even though a CMS like Drupal will automate almost everything you want to do you will invariably need to markup small snippets of text and possibly want to add some custom functionality to your site with your own PHP routines.