navi_1 = new Image();
navi_1.src = 'main/images/navi_1.gif';

navi_1_over = new Image();
navi_1_over.src = 'main/images/navi_1.over.gif';

navi_2 = new Image();
navi_2.src = 'main/images/navi_2.gif';

navi_2_over = new Image();
navi_2_over.src = 'main/images/navi_2.over.gif';

navi_3 = new Image();
navi_3.src = 'main/images/navi_3.gif';

navi_3_over = new Image();
navi_3_over.src = 'main/images/navi_3.over.gif';

navi_4 = new Image();
navi_4.src = 'main/images/navi_4.gif';

navi_4_over = new Image();
navi_4_over.src = 'main/images/navi_4.over.gif';

navi_5 = new Image();
navi_5.src = 'main/images/navi_5.gif';

navi_5_over = new Image();
navi_5_over.src = 'main/images/navi_5.over.gif';

navi_6 = new Image();
navi_6.src = 'main/images/navi_6.gif';

navi_6_over = new Image();
navi_6_over.src = 'main/images/navi_6.over.gif';

function changeImage(ImageID, ImageObject) {
    document.images[ImageID].src = ImageObject.src;
}