The AspNET textbox has a TextMode property which can be single-line, multi-line or password. The contents of a textbox can be in the markup as well, it is between the textbox tags. Take this :
<asp:TextBox id="TextBoxUserName" runat="server" Width="140px">ThisIsMyUserName</asp:TextBox><BR>
<asp:TextBox id="TextBoxPassWord" runat="server" TextMode="Password" Width="140px">ThisIsMyPassWord</asp:TextBox></P>
The good thing is that the contents of a password textbox cannnot be set from markup. In the example the password is still empty. I consider it good because it prevents tampering with a password from markup (The aspx file). The passsword can be set from code-behind
TextBoxPassWord.Text = "ThisMyRealPassword";
A line to delete before rolling out the app.