I can't think of an easy way you could do this using a standard ELF control, and I'm not on Maya to try it out but maybe you could have a text field that was only a couple of pixels high..? small enough so you couldn't see the contents, but big enough to see that it had cursor focus...?
also, I'm not sure if this will work but it worth trying... if you had a textfield that was invisible or unmanaged and that was the one that had focus... then maybe you could create a visible textField that you print a * into everytime the text changes in the invisible field...
the only other way I can think if you really need to do this, is to use a keypad combination instead of a password.. have 10 buttons labelled 0-9 and let the user punch in a PIN number... problem is, some one watching them do it may see which buttons they press...
as for usernames, you know you can get the username from Maya using the command getenv username
:nathaN