For a recent Drupal 6 project, we used Webform (http://drupal.org/project/webform), Salesforce (http://drupal.org/project/salesforce), and Salesforce Webform Integration (http://drupal.org/project/sf_webform) modules to create a custom form to send user data to Salesforce.com. Since the form was too long, we used the pagebreak component in webform to break the form into multiple pages. This not only improves the visual effects of a long form but it's also more clear when the form is made up of different sections.

Currently, we are working on a Drupal 6 project that requires integration with Salesforce.com. We use the Salesforce module for Drupal 6 (http://drupal.org/project/salesforce). We also use the webform module to create the desired form. The data will be sent to Salesforce.com after a user fills out and submits the form.