[Samba] Inconsistent behavior with XP pro clients

[J]

I'm seeing inconsistent behavior with XP pro clients on a Samba PDC.  In 
one case, (a virtual machine) it appears to log in and everything looks 
great.  In another ( a slower PC ), the PC rejects the user login ( even 
with the registry hack ), and in a third, the PC takes a long time to 
"synchronize" not just the user that logged in that time, but all users 
that have logged in since rebooting.

I know this is Windows that I'm talking about, but are there settings to 
toggle for more consistent, reasonable behavior?