Personally, if I were you, with what you are talking about, it sounds like you need to disable this firewall and use something else. I don't think that the MS FW will actually support what you are talking about in a very easy manner.
Though, looking at it, I think if you went into the Security Center, opened the Firewall.
On the "Exceptions" tab, click "Add Port".
In the new box labeled "Add a port" click on the "Change Scope" button. I think that you can add the whole subnet inside of there...
I'm not changing all of my fw settings to confirm this though. Hope that it helps.
In all seriousness though, the MS FW was not designed for complex rules. It is just a simple FW made more or less for home users.