var currenttab;

function SwitchTab(tab)
{
    if (document.getElementById)
    {
        if (tab)
        {
            currenttab = tab;
            document.getElementById(tab).style.backgroundImage = "url(images/buttonon.jpg)";
        }
        else
        {
            document.getElementById(currenttab).style.backgroundImage = "url(images/buttonoff.jpg)";
        }
    }
}