// pre-load images
purelogo = new Image();
purelogo.src = "images/purelogo.gif";

btn_gray_left = new Image();
btn_gray_left.src = "images/btn_gray_left.gif";

btn_gray_left = new Image();
btn_gray_left.src = "images/btn_start_test.jpg";

btn_gray_middle = new Image();
btn_gray_middle.src = "images/btn_gray_middle.gif";

btn_gray_right = new Image();
btn_gray_right.src = "images/btn_gray_right.gif";

btn_yellow_left = new Image();
btn_yellow_left.src = "images/btn_yellow_left.gif";

btn_yellow_middle = new Image();
btn_yellow_middle.src = "images/btn_yellow_middle.gif";

btn_yellow_right = new Image();
btn_yellow_right.src = "images/btn_yellow_right.gif";