Sharing only one private connection, leaving the other public

Hi! I have searched for quite a while about this, and haven't found any
satisfactory answer.
I have Vista x64 and an ASUS motherboard with 2 integrated Ethernet
adapters. One of them goes to a cable modem and the other is used for a
network with 1 other computer. Now on XP I used to have a firewalled, shared
internet connection and a non-firewalled LAN which allowed me to share files,
printers, etc. Now I have a public, shared internet connection, and a private
LAN. Internet sharing works OK.
What has me confused is that when I try to activate file sharing, network
discovery, etc. on Vista, I get a dialog asking me if I want to make my
public connection private (which I don't) or if I want to activate those
features on all public networks as well (which I don't think I want to do).
My question then would be, is there any problem activating those features on
the public connection? Should I do that? Is there any way to activate them
ONLY on the private connection? I don't want a security problem on my hands.
Thanks in advance!