How to access file shares on a Windows Vista computer without entering a password ?

First, make sure that the network is set to "Private" and file sharing is turned on.

To allow access to shared folders without requiring a username and password, you need to modify the network sharing settings, as follows:

1. Click Start, navigate to Control Panel > Network and Internet > Network and Sharing Center
2. Click the "Customize" link under the network heading.
3. Make sure Network Sharing and File Sharing is turned on, if not, enable them.
4. Make sure "Password protected sharing" is turned off, if not, enable it.

Note that allowing everyone access to shared folders does not bypass system security; even though everyone will be able to see the shared files, system may not allow modifications to those files unless they're located in a public place, sucn as the Public folder.