I had to do this recently. The easiest fastest way to do it is to set the text color of the password field to the same exact color as the background of the box your typing it into, such as white. This way as the password is being typed you can't see it. This is how Unix systems and the like do it. No stars, no characters, no nothing.
Otherwise, I don't know how you'd do it, especially with only scripting languages avaliable. If you could interact with your GUI more in-depth, say you had made the whole thing from scratch in Java or C++, you could read each keystroke in, clear the field, and echo back out the right amount of *s.
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Matt Faus
Matt Faus / Microsoft InfoPath MVPQdabra® Software / Streamline data gathering to turn process into knowledge