As far as getting Drupal initially installed and setup, I am going to leave that to other resources (such as http://www.drupal.org.) It isn't too hard, and there are already quite a few sites that go into this in better detail than I could. I will also assume that by now you know how to install and activate modules. If not, check the documentation at http://www.drupal.org.
Also, if following this tutorial completely screws up your website, computer, job, or life, don't blame me. I recommend doing anything like this first on a local test site. You might want to start with a fresh install, just so you don't have anything else that could possibly cause conflicts, or you may setup a local version of your live site. This has the advantage that when you are satisfied with the mod, you can upload it to the server, and be set to go.
I am writing this tutorial using Drupal 6.6, but the process should be similar for other versions.
Activate the following core modules in Drupal under Administer->Site Building->Modules:
You might also want to enable the following, depending on your needs:
With the core modules set, we need to go get some from http://www.drupal.org. By the way, I usually like to install the Nice Menus module right away, even if I don't want it available to the public. It just makes administering the site much easier to have the pop-up menu. Anyway, download and install the following modules: