var how_many_ads = 6;
var now = new Date()
var sec = now.getSeconds()
var ad = sec % how_many_ads;
switch(ad) {
  case 0:
  case 1: content = '<a href="http://computerbooks.tradepub.com/free/ddj/" target=_blank><FONT FACE="Helvetica,Arial" SIZE=-1><B>Dr. Dobb\'s Journal</B></font> (<font color=crimson>free</font>)</a>'; 
          break;
  case 2: content = '<a href="http://computerbooks.tradepub.com/free/swd/" target=_blank><FONT FACE="Helvetica,Arial" SIZE=-1><B>Software Development</B></font> (<font color=crimson>free</font>)</a>';
          break;
  default: content = '<a href="http://computerbooks.tradepub.com/free/orm/" target=_blank><FONT FACE="Helvetica,Arial" SIZE=-1><B>Oracle Magazine</B></font> (<font color=crimson>free</font>)</a>'; 
}
end='></a>';
//if (ad < 3)
//{
document.write(content);