Does Windows allow multiple (remote) logins to the same account at the same time via whatever means?

Yes, but only on server editions (unless you are willing to do some dll hacking). If you are running a server edition un-check the following box under the properties page for remote desktop session host.

Yes it's possible, if you are running a Server version of Windows and you've configured concurrent remote sessions for users.

Client versions of Windows (Home, Pro, Enterprise, etc.) do not allow concurrent, active user desktop sessions of any kind, due to licensing.

Additional info:

• How many concurrent RDP Connections on Windows 7 Pro, Enterprise and Ultimate?
• Is there a way to allow concurrent remote desktop users on XP without changing dlls?
• Concurrent remote desktop in windows with multiple session support