[F5] Using SetInterval

Im back again with another issue -_-. Anyway so the problem is this:
Im creating a thumbnail browser. I want it to scroll when the user hovers their cursor over the up or down button and the thumbnail gallery scrolls respectively. Ive gotten it to work, however I can only figure out how to make it function if the user continuously clicks, and if I use on(rollOver) [Which is what I ultimately want to use] it only moves once, I have a feeling my answer may be using set interval to keep it repeating the action every few milliseconds until the user removes their cursor.

The code thus far is

on(rollOver){
var scroller = scroller -1;
gotoAndStop(scroller);
}

The thumbnails (and buttons that link them) Are in a tweened animation in the same movie clip as this button, so as it increases or decreases the value of scroller, it moves the movie clip one frame forewards, or backwards, making the menu move along the tweened frames. But since Im still new, Ive never used setInterval before and I have no clue on how to implement it to make it constantly execute that script until the cursor has been moved off of the button. Any tips would be great. Thanks alot!