function swtch(num, imgname) {
document[imgname].src = img[num].src;
}
imgsrc = new Array();
imgsrc[1] = "../images/button-1.gif";
imgsrc[2] = "../images/button-1b.gif";
imgsrc[3] = "../images/button-2.gif";
imgsrc[4] = "../images/button-2b.gif";
imgsrc[5] = "../images/button-3.gif";
imgsrc[6] = "../images/button-3b.gif";
imgsrc[7] = "../images/button-4.gif";
imgsrc[8] = "../images/button-4b.gif";

img = new Array();
for (i = 0; i < imgsrc.length; i++) {
img[i] = new Image();
img[i].src = imgsrc[i];
}

function otevrit(theURL) {
window.open(theURL, '', 'width=500,height=700,menubar=no,resizable=yes,scrollbars=yes,left=10,top=10');
}