var randomlinks=new Array()

randomlinks[0]='<img alt="" src="images/blocks/blank.gif" width="150" height="75" />'
randomlinks[1]='<img alt="" src="images/blocks/blank.gif" width="150" height="75" />'
randomlinks[2]='<img alt="" src="images/blocks/blank.gif" width="150" height="75" />'

function randomlink(){
var add = randomlinks[Math.floor(Math.random()*randomlinks.length)]
return(add)
}

document.write( randomlink() );