If you just want to make the textbox show asterisks (*) in the textbox so that the text is hidden when the user types, set the PasswordChar property to *.
That works in all versions of .net framework, and can be done in code or in the winforms designer
the code behind this approach is:
<pre>this.textBox1.Name = “textBox1″;
this.textBox1.PasswordChar = ‘*';</pre>