a = 6 
var slump = Math.random();
var talet = Math.round(slump * (a-1))+1;
function create() {this.code = ''}
b = new Array()
for(var i=1; i<=a; i++) { b[i] = new create() }
b[1].code = ' <td WIDTH=538 HEIGHT=138 BGCOLOR=#000000 BACKGROUND=/images/randombg.jpg> '
b[2].code = ' <td WIDTH=538 HEIGHT=138 BGCOLOR=#000000 BACKGROUND=/images/randombg2.jpg> '
b[3].code = ' <td WIDTH=538 HEIGHT=138 BGCOLOR=#000000 BACKGROUND=/images/randombg3.jpg> '
b[4].code = ' <td WIDTH=538 HEIGHT=138 BGCOLOR=#000000 BACKGROUND=/images/randombg4.jpg> '
b[5].code = ' <td WIDTH=538 HEIGHT=138 BGCOLOR=#000000 BACKGROUND=/images/randombg5.jpg> '
b[6].code = ' <td WIDTH=538 HEIGHT=138 BGCOLOR=#000000 BACKGROUND=/images/randombg6.jpg> '
var visa = "";
visa += ' '+b[talet].code+' '

document.write(visa);