I have made those pages on my Drupal 6: Alpha, Bravo, charlie, Delta. At time of writing, those pages are visible by anybody. I need that those pages are visible only for limited groups, for example: Alpha is visible only for group One and Two Bravo is visible only for group Two and Three Charlie is visible only for group Two and Three Delta is visible only for group Three. I have other nodes and other groups on the Drupal installation that needs to stay untouched, I need to change permissions only for those four pages, and of course their menu links need to reflect that (so each group will see only the menu links that they have granted access) How can I do that?
Try the Nodeaccess module, here is a quote from its project page:
... is a Drupal access control module which provides view, edit and delete access to nodes. Users with the 'grant node permissions' permission will have a grant tab on node pages which allows them to grant access to that node by user or role. Administrators can set default access controls per content type, and also define which roles are available to grant permissions to on the node grants tab.