Simple Telnet chat server
From a once over:

Naming


variable names should start with a lower case letter, unless they are constructors

Server -> server
Cpwd -> password

pwd contains all the connections, any reader would guess it contains passwords


More on variables


There is no good reason to have a separate array ip, since it always contains as many entries as pwd which already contains the the ip addresses in remoteAddress.
Having the password inside your scrip is ok for a prototype, it is not for production


Functions

You encapsulated sendMessage into a function, you should also have a leave or quit function and a joinChat function.

Flow


You announce that a user joins the chat before checking the password
In on 'end' you could just use indexOf on conn instead of manually looping over all connections.


Other than that I think you are doing fine with the asynchronous model of Node.