Are all computers on the same subnet?
As danielhozac asked, is Samba running ('ps -eaf | grep samba') ?
Define 'can't see'. Do you mean the Samba server doesn't show up in network neighborhood? Have you tried:
From a command prompt on one of the windows machines, type 'net view' and press return.
If the Samba server doesn't show up on that list, try 'net view \\SAMBASERVER', replacing SAMBASERVER with the computer name you assigned to the Samba server.
If you get an error there, try 'net view \\xxx.xxx.xxx.xxx', replacing xxx.xxx.xxx.xxx with the IP of the Samba server.
Finally, type 'nbtstat -c'. Does the Samba server show up there? Is the IP correct.
Report your results. Be as specific when reporting error messages as possible.