File sharing and network connectivity control panel applet has been subject to significant changes in Windows Vista. First of all, you get access to all networking options from one window. Network and sharing Center will help you set up sharing options, connect to a network, or configure your internet browser or firewall options in a several clicks.

Obviously, our first step will be clicking on File sharing, choosing "Enable file sharing" and clicking Apply

You should do the same to Printer sharing and Public folder sharing. Very important thing about Windows Vista is that simple file sharing is not enabled by default, unlike in XP. In order to enable it, you basically need to disable password protected sharing.
Other important thing is that when you share a resource (printer or folder), you should specify the user name of the person, you want to share resource with, or enter Everyone to share it for any user. Note, that default access level for a newly added user is reader. Usually, it's enough, but if you want to allow this person to modify your shared files, Contributor should be chosen.