problem in working with onClick event in textbox?

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C#3.0

C#

Hi,
I am working with jquery calender control to display in textbox.My problem is when i use runat="server",the data selected in the calender control is not display in textbox.

Sample code:

Select Date: <input type='text' id='sel'  önclick='dispCal()'  runat="server" size=10 readonly='readonly' />
	<img src="../images/calendar.png"  runat="server"  önclick='dispCal()' style='cursor: pointer; vertical-align: middle;' />
        <table class="calendar" id="calendar" border="0" cellpadding="0" cellspacing="0">
            <tr class="monthdisp">
                <td class="navigate" align="left"><img src="../images/previous.png"  runat="server"  önclick='return prev()' /></td>
                <td align="center" id="month"></td>
                <td class="navigate" align="right"><img src="../images/next1.png"  runat="server"  önclick='return next()' /></td>
                </tr>
            <tr>
                <td colspan="3">
                    <table id="dispDays" border="0" cellpadding="4" cellspacing="4">                        
                    </table>                    
                </td>
            </tr>
        </table>

Here the textbox not shows nothing

Select Date: <input type='text' id='sel'  önclick='dispCal()' size=10 readonly='readonly' />
	<img src="../images/calendar.png"  runat="server"  önclick='dispCal()' style='cursor: pointer; vertical-align: middle;' />
        <table class="calendar" id="calendar" border="0" cellpadding="0" cellspacing="0">
            <tr class="monthdisp">
                <td class="navigate" align="left"><img src="../images/previous.png"  runat="server"  önclick='return prev()' /></td>
                <td align="center" id="month"></td>
                <td class="navigate" align="right"><img src="../images/next1.png"  runat="server"  önclick='return next()' /></td>
                </tr>
            <tr>
                <td colspan="3">
                    <table id="dispDays" border="0" cellpadding="4" cellspacing="4">                        
                    </table>                    
                </td>
            </tr>
        </table>

This code works but i want to use the value of textbox value in codeBehind?
Is possible to work with this?