Samba Madness

We are setting up a new network at work to go along with the new office we are moving to, they want to have access to file shares on the main intranet server which is running ubuntu server with webmin and they dont want to have to use any IDs & PWs. So I set it up to allow all access from anyone using webmin. The down side is this also opens 139 to the net. So I "for now" am going to just block the port at the firewall. I want to set some security in Samba it self but cant seem to find anything that doesnt force the user to input IDs & PWs. Using the firewall is a nice little fix that isnt to messy but any idas are welcome.