// preload images
if (document.images) {
	// off state images
	imgAboutOff = new Image();
	imgAboutOff.src = "./images/button_about.gif";
	imgDomainOff = new Image();
	imgDomainOff.src = "./images/button_domain-knowledge.gif";
	imgProjectsOff = new Image();
	imgProjectsOff.src = "./images/button_projects-implemented.gif";
	imgPTCProductsOff = new Image();
	imgPTCProductsOff.src = "./images/button_PTCProducts.gif";
	imgContactOff = new Image();
	imgContactOff.src = "./images/button_contact.gif";

	// on state images
	imgAboutOn = new Image();
	imgAboutOn.src = "./images/button_about-on.gif";
	imgDomainOn = new Image();
	imgDomainOn.src = "./images/button_domain-knowledge-on.gif";
	imgProjectsOn = new Image();
	imgProjectsOn.src = "./images/button_projects-implemented-on.gif";
	imgPTCProductsOn = new Image();
	imgPTCProductsOn.src = "./images/button_PTCProducts-on.gif";
	imgContactOn = new Image();
	imgContactOn.src = "./images/button_contact-on.gif";

}

function imgOn(imgName) {
	if (document.images) {
		document[imgName].src = eval(imgName + "On.src");
	}
}

function imgOff(imgName) {
	if (document.images) {
		document[imgName].src = eval(imgName + "Off.src");
	}
}