Migrating to Drupal from Wordpress should be a fairly straightforward process for a solid basic transition (complex custom additions to wordpress may need to be re-engineered into Drupal, but your content, comments taxonomies etc should come across just fine)
Suggested steps are;
- Setup a base Drupal site (see our beginning with drupal articles)
- Configure it to your new site as much as you can ( you could install an existing theme or modify an existing theme to your preference )
- Follow the instructions in the Wordpress Import module (read the project page and any text files that come with the tarball) and execute the import
Some things to consider ;
- The visual layout/structure may not be the same, you need to think about if you need custom content types (see the CCK module) or you want to migrate using the default 'page' content type
- Wordpress uses the concept of "categories" but in Drupal they are called "Vocabularies", terms form a taxonomy which belong to a vocabulary, but in the end, they are all the same thing.