var aryImages = new Array(10);

aryImages[0] = "../images/btn_ourmodelOff.png";
aryImages[1] = "../images/btn_ourmodelOn.png";
aryImages[2] = "../images/btn_servicesOff.png";
aryImages[3] = "../images/btn_servicesOn.png";
aryImages[4] = "../images/btn_expertiseOff.png";
aryImages[5] = "../images/btn_expertiseOn.png";
aryImages[6] = "../images/btn_surveysOff.png";
aryImages[7] = "../images/btn_surveysOn.png";
aryImages[8] = "../images/btn_contactusOff.png";
aryImages[9] = "../images/btn_contactusOn.png";
aryImages[10] = "../images/btn_aboutOff.png";
aryImages[11] = "../images/btn_aboutOn.png";

for (i=0; i < aryImages.length; i++) {
var preload = new Image();
preload.src = aryImages[i];
}

function swap(imgName,imgIndex) {
document[imgName].src = aryImages[imgIndex];
}