function getAppVersion() {
appname= navigator.appName;
appversion = navigator.appVersion;
majorver = appversion.substring(0, 1); 
if ( (appname == "Netscape") && ( majorver >= 3 ) ) return 1;
if ( (appname == "Microsoft Internet Explorer") && (majorver >= 4) ) return 1;
return 0;
}
function swtch(num, imgname) {
if (getAppVersion()) {
document[imgname].src = img[num].src;
}
}
imgsrc = new Array();

imgsrc[1] = "images/b1.gif"; 
imgsrc[2] = "images/b1_over.gif";
imgsrc[3] = "images/b2.gif"; 
imgsrc[4] = "images/b2_over.gif";
imgsrc[5] = "images/b3.gif"; 
imgsrc[6] = "images/b3_over.gif";
imgsrc[7] = "images/b4.gif"; 
imgsrc[8] = "images/b4_over.gif";

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