I hope you are looking for this multi select module http://drupal.org/project/multiselectMulti Select module.
The Multiselect module defines a widget to be used with CCK fields. It allows the user to select multiple items in an easy way. It consists of two lists, one of all available items, the other of selected items. The user can select an item by moving it from the unselected list to the selected list. This module relies on the built-in jQuery features of Drupal and does not require any additional modules other than the CCK module set (Drupal 7 version has no dependencies).
