http://www.google.com/support/forum/...de5902fd&hl=en

This code works for me;

Code:
javascript:
timeout=prompt("Set timeout [s]");
current=location.href;
if(timeout>0)
  setTimeout('reload()',1000*timeout);
else
  location.replace(current);
function reload(){
  setTimeout('reload()',1000*timeout);
  fr4me='<frameset cols=\'*\'>\n<frame src=\''+current+'\'/>';
  fr4me+='</frameset>';
  with(document){write(fr4me);void(close())};
}
Click the bookmark with the tab you want to auto-reload active.
Set the time interval (in seconds) or set it to zero to cancel auto-reload.

there are other modifications available though