OD + Windows Authentication has failed

I have 4 identical XServes at our school district, each running 10.4.11 Server XServe1 is OD Master and PDC XServe2, 3, and 4 are all OD Replicas, BDC and host student Home Directories. Windows Profiles also reside on XServe 2, 3, and 4. This setup has worked almost flawlessly for 18 months. Yesterday we had technicians setting up 6 new Windows Machines with XP SP 3 (this may be coincidental but I mention it just in case) Everything is still just fine for authentication from Macs. Windows now are intermittent. A student may be able to log in just fine. If he or she then logs out and comes back to same or different machine they may or may not be able to log in. They get a message that says they can't locate the domain or that their name/password is incorrect. In many cases, if I change the password from Workgroup Manager and then force replication they can often log in again. If they then log out, they may or may not be able to log in again. If they go to a different machine they may or may not be able to log in. I can find no way to "force" this to happen, and can't predict which machine it will happen on. My first guess is that Password Server isn't working?? I can't confirm at all Anyone have any clues on what I can do to try to fix this? thanks Bart