How to validate the date already appered on gridview or not?

Question

Hai friends,
       
       Im creating one application in that using jquery datepicker (calender) my input details are given below:

date:(calender)
from:(textbox)
to:(textbox)
remarks(textbox)
add(button)
after adding the details entire details ll show on Gridview's.

(Ex:
 date:02-apr-13,
 from:banglore,
to:pune
apply(add)
the details ll show on GridView,now if im choose same in calender ll show error mess" already the date was appeared".)
how to validate the input date and already appread on gridview