Can a domain have two set of users.... let me explain the situation.

mydomain.com has a set of users which have admins etc etc.

can i have sub.mydomain.com with the same set of users, with different admin and restricted access to certain level.

If they are users on the server you should be able to granulate the security. Just make sure you don't put the users in a group which allows them total access. Have a group for each domain and add users to those groups as needed.

Active Directory? OpenLDAP? What?

-Chris

The question seems to be related with Active directory structure

Yes, you can get pretty granular with your user permissions and rights with active directory. Depending on what your needs are, you can utilize the built-in domain groups or build your own custom priviledge sets with custom groups and GPOs. It really depends on what the users need access and rights to do. It could be simply file and directory permissions or more complex integration with GPOs.

if it's referring to the online website, I think it's possible. you can dump the users to new location manually though.