In the two guides I have written (so far) on sharing files between Macs and Vista PCs, Sharing files between a Windows Vista Home Edition PC and a Mac running OS X Leopard 10.5 and Sharing files between a Windows Vista Business Edition PC and a Mac running 10.4� I did not disable password protection on the Vista PCs.
This meant that users sharing files needed to enter a password (or have a matching account) in order to access shared folders on the Vista PC.
However if you turn off password protected sharing it is possible to share files without for the user on the remote computer who is accessing the shared folder to use a password.