I just installed a fm12 host on windows 7 last week
this is what I did ... I hope it has an answer to your question
1.got to control panel, programs and featurs... turn windows features on
turn on telnet both server and cleint
2. go to command prompt and issue telnet localhost 5003
3. In control panel again go to internet,, windows firewall and click on allow a program or feature through windows firewall
then put a check mark opposite to filemaker
Port 5003 is the only port you should have to open, then set port forwarding to your ip address for access outside the local network.
My windows firewall has two inbound Rules for FileMaker Pro Advacned, 1 with Protocol type TCP with all port on local and remote open, 2 with Protocal type UDP with All ports on local and remote open. I haven't tried changing the setting to just 5003, but I would guess that should work. I just forward port 5003 from my router to the ip of the computer hosting the database.
I figured this out on my own after I posted. I knew about port 5003, but didn't see how to get to the right part of the control panel to set it. Part of the problem was that I was looking at "incoming" rules--which W7 had already set up since the computer is usually a client of other DBs, instead of "outgoing" rules. Once I looked there and saw that there were none that listed FileMaker, I was able to add a new rule and specify the 5003 port.
It then took a restart of my computer--maybe I just needed to close and re-open FileMaker, but the restart did that too so I was covered either way and once I had the hosted file back open, my iPhone could use Go to access the hosted file and this makes for a very quick/convenient way to test a new version underdevelopment without having to copy it over to the iPhone each time. (I've been teaching my self different Go tricks and tips by creating some DB's designed to work on the iPhone--one of which is the Known Bugs List Database which now has iPhone friendly layouts for those who wish to keep that tool handy as they move from job site to job site.