I (had) a working Samba PDC with several joined Win2K clients (and a WinXP machine), and everything functioned correctly up and until I disjoined one of the Win2K machines.  There-after I cannot rejoin that machine nor join any new machines.  I havn't tried disjoining the XP machine to rejoin it as of yet.  (I can if that's of any use for testing purposes to you).

A level 10 log is available here: http://www.plfc.co.uk/level_10_log , that is a sniplet of the log starting from before attempting to join a machine until after it fails.  Again, I can get more detailed / more complete logs as requested.

The Windows 2000 clients request the username and password to join the domain as expected, but then fail to join with "The remote procedure call failed"

I've posted a lot of information already on the Samba mailing lists, so to save much time and effort, I will simply link to that thread from here:

http://lists.samba.org/archive/samba/2006-April/subject.html#120408

Thanks,  Matthew Hall