Hey haynboi , tell you what it sounds that your Network Topology looks like many small companies's
=> A private Network (Where you required Netbios for Network Neighborhood facilities and other M$ win stuff...)
=> And something similar of what is called DMZ (A DMZ could be a Firewall on its own!).

I'll advice you to have a quick googling about DMZ and you should be able to build your network architecture on your own.
this url may help

http://nsupport.elronsoftware.com/su...1?OpenDocument

Provided you dedicated a hw (pc or whatever) I will advice you to use it as firewall and disabled every single ports and then open one by one those required for your external to DMZ flows.