Itunes query

[Scott Rutkowski]

Hi All.

I'll be buying an Imac 20 inch on the weekend and am really looking forward 
to it.
My question is with Itunes when you click on the price of a song you would 
like to buy, you get a dialog box that comes up asking if you would like to 
purchase the song. there's also a checkbox that says don't show this again.
I've accidently ticked the box on my friend's Itunes and we want to reverse 
the option so the dialog box about if you want to purchase this song 
reappears instead of Itunes just going ahead with the purchase.
can anyone on the list tell me how this functionality can be restored 
please?

Thanks.