Enter Only Alphabet Characters in textBox Using JavaScript

function AllowAlphabet(e) {

            isIE = document.all ? 1 : 0

            keyEntry = !isIE ? e.which : event.keyCode;

            if (((keyEntry >= '65') && (keyEntry <= '90')) || ((keyEntry >= '97') && (keyEntry <= '122')) || (keyEntry == '08') || (keyEntry == '46') || (keyEntry == '32') || keyEntry == '45')

                return true;

            else {

                alert('Please Enter Only Alphabet Characters, Not Numbers and Special Charactors .');

                return false;

            }

        }

<asp:textbox id="txt_Name" runat="server" onkeypress="return AllowAlphabet(event)" ></asp:textbox>