This became an unnecessarily complex thread in a hurry! Is it my
imagination, or did it just go off on a crazy tangent?
Run the network setup wizard (from the common task pane in Network
Connections or My Network Places, "setup up a home or small office
network") on all three computers, choosing an identical workgroup name
for all three computers. (You can skip the network setup disk thing at
the end of the wizard.)
That should be enough to cover all of the bases. After running the
network setup wizard, give the PCs a couple of minutes to negotiate
among themselves. (One of the really annoying things about setting up a
Windows peer-to-peer network is that it doesn't respond instantly to
changes in settings; if you are not patient, you can end up chasing your
tail right past the point where it would have all worked.)
What follows is just assurance, but it does give you something useful to
do, while waiting for the PCs to work out their networking among
themselves.
After running the wizard, on each PC, go to Network Connections in
Control Panel. Remove any bridge connections, which might have been
accidentally created by the wizard. (It is not uncommon to end up
bridging 1394 and ethernet, which is silly!) (You can also remove any
virtual connections, which might be left over from a previous life with
DSL or AOL or whatever.) Then, check the properties of the active
Ethernet Connection to your network.
You should have, in each case, Client for Microsoft Networks, File and
Print Sharing, and TCP/IP, and maybe, QoS. Remove any other network
protocols. Check the properties of TCP/IP. (You might want to specify
the DNS servers prescribed by your ISP on the general tab, though this
is purely optional and irrelevant to your immediate problem.) Click on
the Advanced... button under the General tab, and then find the WINS
tab, and check Enable NetBIOS over TCP/IP.
While still in the properties of the Ethernet connection, go to the
Advanced tab, and make sure the Firewall is turned off (clear the
checkbox).
If you have a third-party firewall program (e.g. Norton Firewall in
Norton Internet Security, McAfee, Zone Alarm, etc., then you must
configure that program to allow access to the network address range of
your local network.
Go to Start, then Run. Type cmd and press enter, to open a DOS box. On
the DOS command line, type
ipconfig /all
The result should include the ip addresses of your PCs. I would expect
an address such as 192.168.2.101, as assigned by the SMC router, with a
gateway (i.e. the local ip address of the SMC router) such as
192.168.2.1
By now, you should be exhausted, but happy.