Hi, Mike,
Don't know if this will help, but the Winforms textbox control has a property called 'PasswordChar'. I usually set it to an asterisk(s) for something like that. You can also do something like...
textBox1.PasswordChar = '\u25CF';
Give that a try and let me know if that works for you. I use a small form to prompt for user id and password, I've never tried an inputbox for something like that.
Kevin