I'm not on a linux machine right now (I am deployed to Iraq and sitting in a free cyber cafe!) So I can't play around with Samba. I normally use nfs but here is basicly what you need to do.
1.) Document all commands that your PDC Admin routinely or will at some time use.
2.) Create a group named sambadm and add all of the users you want to be samba admins to this group.
3.) Create a '/etc/sudoers' file and add all of your permissions to it.
The format for the /etc/sudoers file is very simple
username host = command
Here is an example:
%sambaadm PDC = /usr/bin/smbpasswd,/usr/sbin/useradd,\
Now the user just types 'sudo smbpasswd' or whatever they need to type. It will prompt them for their own password and then will execute. If you use the NOPASSWD option like the one listed in the last link, they won't even need a password. I hope this helps
check this out for some ideas