The AJAX FilteredTextBox is a very easy way to extend an asp.net text box so that it doesn’t allow certain characters.
http://www.asp.net/ajax/AjaxControlToolkit/Samples/
To install the Visual Studio IDE controls, create a new category and add controls by browsing to the ajaxcontroltoolkit dll.
An example of how to use the filter exender is below.
<ajaxToolkit:FilteredTextBoxExtender ID=”ftbe” runat=”server”
TargetControlID=”TextBox3″
FilterType=”Custom, Numbers”
ValidChars=”+-=/*().” />
<asp:TextBox id=”txtbxExample1″ runat=”server” />
<ajax:FilteredTextBoxExtender ID=”ftbe” runat=”server” TargetControlID=”txtbxExample1″ FilterType=”Numbers” />