Hi mpaige

one way to sort of do it would be to use a new layer with the larger image on. Select the thumbnail and then click the webproperties (link icon) >mouse over > radio button select it to show the pop up layer. if you name the pop up layer (fade-in 3)(fade-out 3)nameofpopuplayer number 1 to 5 can be used can give a speed effect of dissolving in and out but will not grow out and enlarge this may need to be hslide/javascript/jquery. one of the other members could perhaps help.

you can also use a mouse click command and add lock (fade-in 3)(fade-out 3) to the layer name this will pop up and lock but you need a close button icon or text e.g on the large image a 'x' text or graphic and link it to web adress put popup:close.