network permissions

I have four computers running XP, all connected to an
ethernet hub. When we first set it up, everything worked
instantly. We each installed McAfee Personal Firewall
and are now having problems seeing eachother and sharing
files on the network. All our connections are set
to 'obtain IP automatically', I have tried everything
suggested on various websites. One computer connects to
broadband internet through the hub (the cable modem
connects to the hub).

Ultimately, we with to share this internet connection
(internet connection sharing is enabled also) but right
now cannot even share files. Some of the computers
(including the one connected to the internet) do not have
access to the workgroup MSHOME of which all computers are
members.

How can I change the network permissions? We've all
uninstalled the firewall but could it have changed some
of the security settings on our machines?

Help appreciated!