calendar and textbox should disabled...

i am using an calendor and textbox.

when i choose a date from calendar it should display in textbox and it's happening too.

my problems is user can enter a value in textbox also. i want to disable textbox.

i am using input control.

i tried  to make it readonly. but my calendar image also became readonly.

here is my aspx code.

<td width="55%" class="titleMinor">
                       Debt - good through :
<A HREF="_javascript: void(0);" ONCLICK="var g_Calendar = new Calendar(new Date(),true);g_Calendar.show(event, '<%= txtDebtDate.ClientID%>', false, 'mm/dd/yyyy');return false;"><IMG SRC="/image/icons/icoCalendar.gif" WIDTH="19PX" HEIGHT="16PX" BORDER="0PX" ALT="click to view calendar" ...