function getOperaVersionNumber() {
	var ua = navigator.userAgent;
	var OperaOffset = ua.indexOf("Opera ");
	if (OperaOffset == -1) 
		return 0;
	else
		return parseInt(ua.substring(OperaOffset + 6, ua.idexOf(" ", OperaOffset + 6)));
}

function getNNVersionNumber() {
    if (navigator.appName == "Netscape") {
        var appVer = parseFloat(navigator.appVersion);
        if (appVer < 5) {
            return appVer;
        } else {
            if (typeof navigator.vendorSub != "undefined") {
                return parseFloat(navigator.vendorSub);
            }
        }
    }
    return 0;
}

function getIEVersionNumber() {
	var ua = navigator.userAgent;
	var MSIEOffset = ua.indexOf("MSIE ");
	if (MSIEOffset == -1) 
		return 0;
	else
		{
		var to  = ua.indexOf(';', MSIEOffset + 5);
		var ver = ua.substring(MSIEOffset + 5, to)
		return parseInt(ver);
		}
}

function isPNGSupported()
	{
	var isMac;
	var ieversion;
	var nnversion;
	var operaversion;
	var pngsupport;
			
	pngsupport = true;
	
	operaversion = getOperaVersionNumber();
	//document.write("OPERA VERSION NUMBER = " + operaversion);
	if ((operaversion !=0) && (operaversion <= 4))
		pngsupport = false;

	nnversion = getNNVersionNumber();
	//document.write("NAVIGATOR VERSION NUMBER = " + nnversion);
	if ((nnversion !=0) && (nnversion <=5))
		pngsupport = false;
		
	isMac = (navigator.userAgent.indexOf("Mac") != -1);
	ieversion = getIEVersionNumber();
	//document.write("IE VERSION NUMBER = " + ieversion);
	if ((ieversion != 0) && (ieversion <= 6) && (!isMac))
		pngsupport = false;
		
	return pngsupport;
}

function swapGIFtoPNG()
	{
	var gifimage = swapGIFtoPNG.arguments[0];
	var pngimage = gifimage;
	var gifplace = gifimage.indexOf('gif');
	
	if (gifplace >= 0)
		pngimage = gifimage.substring(0, gifplace) + 'png' + gifimage.substring(gifplace+3);
	
	return pngimage;
}
	
function loadPNG()
	{
	var logoimg;
	var navimg;
	var mystyle;
	var buttons;
	var i;
	
	if (isPNGSupported())
		{
		if (document.images)
			{
			
			logoimg = document.getElementById('logo');
			if (logoimg)
				logoimg.src = swapGIFtoPNG(logoimg.src);
				
			buttons = new Array('nav-homebutton','nav-cheatbutton','nav-top10button','nav-weatherbutton','nav-feedbackbutton');
			for (i in buttons)
				{
				navimg = document.getElementById(buttons[i]);
				if (navimg)
					{
					mystyle = window.getComputedStyle(navimg, null).backgroundImage;
					navimg.style.backgroundImage = swapGIFtoPNG(mystyle);
					}
				}
				
			}
		}
}