Scrolling mc problem...HELP PLEASE!

1

[FONT=Arial]Hey there everyone. I have a blank mc that has thumbnails nested in it, that scroll up and down onPress of an ‘up’ button and a ‘down’ button. The thumbnails are 40x40 and there is a 5px space between them and they move up or down in 5 rows at a time. (I set the thumbnails to move (with an ease) 225 pixels up or down when you press the up or down button.)

The only problem I am having is when you click the up or down btns repeatedly. If the thumbnails have not finished easing into place when you click the up or down btns again, it will add another 225px to wherever it is currently at. This makes it so that sometimes only half or part of the thumbnail is inside the mask. I need to somehow disable the up or down btn after being pressed, until the thumbnails are finished moving into place.
sorry if that sounds confusing. Any advice will help. Here is my code. THANKS[/FONT]

//easing function------------------------------------------
yPos = 0;
#include "lmc_tween.as"
function boxMove(yPos) {
    yTo = thumbnailCont_mc._y-yPos;
    thumbnailCont_mc.slideTo(null, yTo, .2, "easeInOutQuad");
}
//-------------------------------------------------------
//scroll thumbnails up
btnUp.onPress = function() {
    boxMove(-225);
};
//scrollthumbnails down
btnDown.onPress = function() {
    boxMove(225);
};