Populating Hidden Fields in a Form

Populating Hidden Fields in a Form

I have a form with an inputbox and the value of that input box needs to be also assigned to a hidden field.
    <TD>City</TD>
                    <TD WIDTH=10 align="Right">:</TD>
                    <TD><INPUT TYPE="Text" NAME="Contactcity" ID="Contactcity" VALUE="" tabindex="9"></TD>

Here is the hidden field I need the above value assigned to.

<INPUT Type="Hidden" Name="LEADSCity" Value="">

Thanks