old/new systems can't see each other

I just added three systems to a peer-to-peer and just have a few
important quirks. I'm not a novice but don't know the answer here.

All XP. Connected to a DSL modem/router. Router settings are default.
New 3 systems are default (get IP from DHCP etc). All on the same
workgroup. The three old systems can see each other but not see the
new ones. The new ones can see each other but not the old ones. There
are a couple network printers, the new ones can see but not the old
ones. When I say "see" I mean they don't show up in network
neighborhood. I can manually type in the name of a printer shared by
an old system and the new one can connect to it. All can print to the
printers even if they can't "see" them. I cannot force a new system to
connect to a shared folder on an old one, even when using IP address
and typing in the share name. So the one old one that acts as a file
server (just a shared disk) cannot be accessed by the new ones. They
can all get out to the internet. Two of the old ones are also on auto-
ip etc. One is fixed. Not sure if the guy who set it up had some
reason for that. No firewalls on systems.

Maybe the guy who set it up (who is not around now) made some
restrictions? One old system tries to boot directly into a particular
logon even though there are several logons and all have passwords.
(All systems have a JoBlow administrator logon and a Student limited
logon.) I've even eliminated the old logon it wants to use and created
a new one and it still tries to logon to the old name, or it gets hung
up trying. So maybe the guy who set it up locked some things down but
I'm not sure how.

Any ideas?

Thanks,
Tom