var n = 14;
var f = false;
var b = new Array;

function prel()
{
    if(document.images)
    {
        for(i=1;i<=n;i++)
        {
            str = 'buttons/b' + i + '_o.gif';
            b[i-1] = new Image();
            b[i-1].src = str;
        }
    f = true;
    }
}

function on(im)
{
    if( document.images && (f == true) )
    {
        document.images[im].src="buttons/"+im+"_o.gif";
    }
}

function off(im)
{
    if( document.images && (f == true) )
    {
        document.images[im].src = "buttons/"+im+".gif";
    }
}