Try totally disabling the firewalls and all antivirus (some antivirus products also have firewalls).
Use the command tool to 'ping' the IP address of the remote machine. If you can see it on an IP ping, try pinging the name.
If the address works, you have connectivity. If the name works, you have name resolution. If those work but you can't browse, try doing a 'map network drive' from tools on My computer, using address ' \\remotename\remotesharename' where 'remotename' can be either the host name or an IP address.
If you can mount but still can't browse through microsoft networks (see your workgroup computers) there is definitely something blocking the traffic and it can only be on one or other of the computers if you are running over a hub.
BW