You need a CMS.. Of which there are 2 main routes you can go down:
- Build it yourself
- Use a 'ready made' CMS such as Wordpress, Drupal, or a Forum with a CMS plugin such as Simple Machines Forum (SMF - formerly YaBBSE and YaBB)
IF you are choosing to make it yourself then expect a learning curve. You will probably need to learn a bit of Javascript, a lot pf PHP and get ready to hand code any HTML.
It's not an easy task, but if you want to do it I would suggest:
- tizag http://www.tizag.com
- google 'php content management systems' and find a tutorial (e.g. http://www.intranetjournal.com/php-cms/)
I would recommend MySQL for starters instead of XML, though you can get nearly the same base functionality out of an XML file as a MySQL DB (MySQL has a number of functions and is better overall than XML... but XML will do if you just want to store data in a flat file).
Good luck, and remember this is the place to ask questions... So if you choose to learn PHP and don't understand why something isn't working, or don't grasp a concept... Give us all a shout :)
http://www.php.net <- useful...