[Samba] protocol question

[l. a. walsh]

I'm trying to understand odd behavior in my LAN.  I'm running Samba
2.2.5 and trying to run it as a PDC. 

I have 1-2 win98 clients, 1 XPSP1 client, and 1 Win2kSP3 client.

I've managed to add the XP and 2K machines to the domain successfully,
but
still haven't finished configuring logins to work correctly -- something
about my user not having permission to write to \\server\uname\profile
even though permissions on the various login paths and and netlogin
shares would seem to be in order -- but I can play more with these.

My main question concerns ethereal trace output:

Quite often when My w2k client is doing a lookup on my local group, I
see:

w2k -> server NBNS "Refresh MYGROUP <1d>"
server -> w2k ICMP "Destination Unreachable"
or more often:
w2k -> server NBNS "Name query NB MYGROUP <1c>"
server -> w2k ICMP "Destination Unreachable"
(repeated several times per cycle)

So why is the supposed (?) PDC, "server", sending back ICMP packets --
I thought ICMP dest unreachable's were for IP routing?  Why am I seeing
them in response to a NBNS refresh and name queries?

Is this too technical for this group?  It's sorta a 'newbie' question,
since
I'm just starting to understand this stuff, but am not sure where the
tech/regular list dividing line is....

Thanks,
-linda