Ubuntu snag

Hello! If you have been following this blog at all, you know that I am working on playing with Ubuntu in the classroom. I am using Ubuntu 8.04 LTS (the current version as of this post is 10.04) because it is the software that works with the NComputing boxes that allow virtualization. Well, as is usually the case, I have hit a snag that I can't get around right now. Like most people I have a Windows environment in my school with a server running Active Directory. All of the students log in to the server using their username and password and I control policy and so forth using Group Policy for each grade. Well, I am trying, unsuccessfully at this point, to integrate the AD with my Ubuntu box. I have read about Samba and I even found and downloaded the GUI (Graphical User Interface) program SADMS which automates much of the process (it edits the necessary files for you after you provide pertinent information). However, I keep getting an error message about changing the password on the server before I can get a Kerberos ticket. I can ping the AD server and I sync time servers so it isn't either one of those problems. I have changed password several times to no avail.
So, I am putting out a plea for help. If anybody has any leads or can direct me somewhere, I would be very appreciative.
I would also love to hear about any successful (or unsuccessful) OpenSource integrations into a classroom setting if someone would like to share!