I will be answering in English so more people will find this post useful. However, if there is anything you don't understand in my comment, I can change to Spanish.
What I would do is install modules of Drupal on top of the stack you already have. Here you can download one of those. (you can install as much as you want)
Also, you have two options for this: using different domain names (i.e.
www.weba.com goes to Drupal installation A and
www.webb.com goes to Drupal installation B, both on the same machine and server) with virtual hosts, and using prefixes (i.e.
www.web.com/a goes to Drupal installation A and
www.web.com/b goes to Drupal installation B.
If you have any doubt, please don't hesitate to write us back. We'll be more than glad to help you again!