Mac File Sharing with Windows 7
When connecting to a Mac from a PC for file sharing, you should be able to use your full username that shows up on your login screen and the password associated with it. For example, when connecting from a PC to a Mac someone with the username "John Doe" would sign in using that as the username. They would use their password associated with that account as their password, but make sure that that account is enabled in System Preferences to support SMB file sharing, because if the account is not enabled, then you cannot log in. Here is a screenshot of what I mean: