Apple took out the groovy util they had in DP4 which made it *really* easy to do all this. Now, you have to alter the NetInfo database directly. Here is what you do:
1. Run up /Applications/Utilities/NetInfoManager
2. In the window that comes up (looks sort of like the NeXT file browser, as it should, since NetInfo was an OpenStep creation), go to /groups. In the thid column will be a list of the user groups that exist thus far.
3. Select one of the groups (admin is a good example one). A list of properties and values will appear below. Each group has at least these properties: `passwd', `gid', and `name'. `passwd' should be `*' for all of the groups. If you don't know what gid and name do, then you shouldn't be messing with groups. (Although you sound like you know already). Some groups have a fourth property: `users', which has, as its value(s), user names.
4. To add/remove a user, add/remove their name value from the `users' property. If you want to add, you do it by selecting hte property and choosing "append value" from the "Directory" menu. Note: make sure you click the lock in the bottom left to make changes!
5. To add a user group, you can either create a new directory in /groups of the NetInfoDatabase, and add all the proper attributes, or, more easily, Duplicate an existing one, and change the name and gid. Then, add and remove users as desired.
6. IMPORTANT: You won't be able to use your changes unless you either (a) restart, or (b), choose to restart the NetInfo Server from the "Options" menu.
7. You should be able to `chown' directories (that are not on a classic drive) from su with no problems!