open calendar control in new form

Hi

I got this bit of code from 4 guys from rolla website

Code:

<form name="frmCalendar"> <input name="txtDate" type="text" /> <a href="javascript:calendar_window=window.open('/calendar.aspx?formname=frmCalendar.txtDate','calendar_window','width=154,height=188');calendar_window.focus()"> Calendar </a> </form>

How do i get this to work in code behind as i want it to open the new window when i click on an asp.net button.

Many thanks
Nick