show image on mousehover asp.net imagebutton

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......