asp.net mouseover

Question

I am using a datalist control for displaying ThumbImage.....i want to when user

mouseover on datalist image........ it's show original image

first div is for displaying Original Image....for showing image here i m using asp:image controls

 Second Div,.....here i bind the datatlist (here it only displaying the ThumbImage)

 my problem is that....i cant understand....how i display image on mouseover of datalist ThumbImage

       .....Pl'z suggest me......