Can you give a bit more information about which errors you encounter, in the log or the client, and what actions you did perform?
Furthermore, in addition to the the guide: After setting up the server configuration, you should perform 'read ldap' and when the read operation finishes, perform 'browse LDAP'. You now can browse to the unit you want to import. Select 'set as LDAP import location' when you are inside the directory you want to import (that is, you can acually see the users which will be imported).
The next steps are to synchronize the groups, set up the group mappings and finally import the users. Note that each of these steps is necessary. Furthermore it is very important that the LoginField is set (usually sAMAccountName will do).
If I understand correctly, you have no problems importing from one location in LDAP, but you want to import from multiple locations?
In that case you need to create multiple LDAP servers (each connecting to the same server) but configure different locations for each server. That will import users from multiple OU's.