No, you can't use a password to protect files and folders in Windows. However, some programs that run on Windows do allow you to protect individual files by using a password. For more information, check the Help for the program you are using.
There are other ways to protect your files and folders in Windows. You can encrypt your files, manually specify who can access the folders or files, or hide them. Choose your method based on how secure the folders or files need to be. Encrypting is the most secure, while hiding the folders is the least secure.
The ability to encrypt files and folders is not available in Windows Vista Starter, Windows Vista Home Basic, and Windows Vista Home Premium.