How do I achieve 2 level tabs?
If you have a theme that supports the output of primary and secondary links in the way you describe (Bartik, the default theme for Drupal 7 does, but it doesn't have the secondary nav below the primary, but rather in the upper right of the header), you can accomplish this by setting the secondary menu to be the same as the main menu. Navigate to admin/build/menu/settings to make this selection.

You can further customize this behavior using the Menu Block module.