samba - Feb 2007 - domainusers cannot access printer on some other machine in the domain

I've a running Samba 3.0.22-Server which serves as fileserver an das PDC for
the
local domain with approx. 20 XP-Clients. Everything working fine.

Now some XP-Clients have local printers installed and I share them so that other
  machines can use them. Unfortunately it does not work, cause my users are not 
permitted to access this client.

example:

domain : MYDOMAIN
client1: has a printer installed
client2: user MYDOMAIN\nick is logged on and tries to access client1 to connect 
to the printer. Now nick is asked to provide a username and a password and 
nothing seems to work MYDOMAIN\nick nor nick.  Only if I provide the 
admin-access of client1, it would work : CLIENT1\administrator, but this is 
definitely not what I want.

Before this new samba3-server I used a old samba2-server and I didnt had any 
problems then. The clients stayed the same, so I think its a samba-problem but I
dont even know where to start looking.

any hint appreatiated
thnx
peter