If you're a WordPress user and have been wanting to get into Drupal, you should check out this guide on hokuten.net. It gives you information on two main points - installation and theming.

Anyone who has worked with both knows that anything you can do in WordPress, you can do in Drupal, and vice versa. It just takes some elbow grease. [Drupal] is a great thing to learn because of its broad market, but WordPress developers might find some difficulty getting acclimated—Drupal has a much higher learning curve.

They mention some of the differences between the installation of the two (creating settings files, making additional directories) and a table showing the correlating theme files between the two.