Multistep adds multiple-step functionality to content type editing forms. It does so by assigning a step number to each fieldgroup within the content type and hiding all the groups that do not belong to the current step. The user can then use different submitting buttons that will redirect to the previous, next, or current step.
The module also provides a block for each content type with a menu of the different groups within that form and a progress bar. This provides an easy way to jump to different steps throughout the form without having to go one by one and to keep track of you progress through the form.
Read the documentation for usage and configuration options.
The Drupal 7.x branch depends on the Field group module. Configuration is now done directly on the Manage Fields page, by adding Fieldgroups of type Step, rather than manually assigning the number of a step to a group.
The Drupal 6.x branch depends on CCK and Fieldgroup (part of CCK).