Need help on hitting "Enter" key to trigger a button...

Hi,

I'm trying to make the "Enter" key function exactly the same as clicking on the Find button that has an ' OnClientClick="return validateForm()" ' and does a PostBack. In other words, if the user hits the "Enter" key on his keyboard after filling in the zip code, I need the "Enter" key to do exactly as clicking on the "Find" button.

Thanks very much in advance.

<script type="text/javascript" src="/js/jquery-1.2.1.js"></script>
    <script type="text/javascript">
        // <![CDATA[
        function validateForm() {
            var zipCode = $("input#<%= txtZipCode.ClientID %>").val();
            zipCode = $.trim(zipCode);
            var state = document.getElementById("<%= ddlState.ClientID %>").value;
            var objZip = document.getElementById("<%= txtZipCode.ClientID %>");
            if (zipCode == "" && state == "") {
                alert("Please enter a zip code or select a state!");
                objZip.focus();
                return false;
            }
            if (zipCode != "" && !validateZipCode(zipCode)) {
                alert("Please enter a valid zip code!");
                objZip.focus();
                return false;
            }
            
            return true;
        }
        
        function validateZipCode(v) {
            var regex = /^\d{5}$|^\d{5}-\d{4}$/;
            return regex.test(v);
        }
        // ]]>
    </script>		
 
    <div>
	<form id="form1" runat="server">
        <table border="0" cellpadding="2" style="width:500px">
            <tr id="trZip" runat="server">
                <td style="text-align:right">Please enter a zip code</td>
                <td style="text-align:left">
                    <asp:TextBox ID="txtZipCode" Width="40px" MaxLength="5" Runat="server" />
                </td>
            </tr>
            <tr id="trOR" runat="server">
                <td style="text-align:right">OR</td>
                <td>&nbsp;</td>
            </tr>
            <tr id="trState" runat="server">
                <td style="text-align:right;vertical-align:top">Select a state</td>
                <td style="text-align:left">
                    <asp:DropDownList 
                    ID="ddlState" 
                    DataSourceID="srcState" 
                    DataTextField="StateName" 
                    DataValueField="State_ID" 
                    AppendDataBoundItems="true" 
                    Runat="server">
                    <asp:ListItem Text="Select State" Value="" />
                    </asp:DropDownList>
                    <br /><br />
                    <asp:Button ID="btnFind" Text="Find" OnClick="btnFind_Click" OnClientClick="return validateForm()" Runat="server" />
                </td>
            </tr>
        </table>
		
        <asp:ObjectDataSource
            id="srcState"
            TypeName="State"
            SelectMethod="SelectStates"
            Runat="server" />
	</form>
    </div>

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