This is a serious flaw, one of many, in Vista networking, which many users
encounter because Vista does not have any rational wizards to walk users
through the process of setting up a peer to peer network and defaults to
illogical settings.
Worse comes when users who are not IT professionals want to share anything
other than the "public" folders.
Apple users have less problems not because the hardware or network protocols
are any better but the setup routines do not require Microsoft Networking
certification.
Of course if you want to do more than small peer to peer networking using
Apples you are SOL and will rapidly go broke paying for hardware at 2 to
three times its actual retail value . . .