function showTab(tab, contents) {
    document.getElementById('tabScrn').setAttribute("class", "menulinks");
    document.getElementById('tabGuide').setAttribute("class", "menulinks");    
    document.getElementById('tabHandset').setAttribute("class", "menulinks");
    document.getElementById('tabReview').setAttribute("class", "menulinks");

    document.getElementById('appScrn').style.display = "none";
    document.getElementById('appGuide').style.display = "none";    
    document.getElementById('appHandset').style.display = "none";
    document.getElementById('appReview').style.display = "none";
    document.getElementById(contents).style.width = "434";
    document.getElementById(contents).style.display = "block";

    document.getElementById(tab).setAttribute("class", "menulinkschoice");
}