> Or are you talking about some command-line shell that prompts you with an underscore?
In Windows, the command for that is "prompt" followed by the new prompt text
C:\>_
C:\>prompt blah blah blah_
blah blah blah _
I dont think you can do this programmatically.
You could futz around with Runtime/Process or JNI.
The new Java 6 Console class doesnt seem like much help
though actually readPassword and readLine allow you to set
the prompt text.
http://java.sun.com/javase/6/docs/api/java/io/Console.html