Ti faccio un esempio semplice... a te abbellirlo
codice:
<script>
function descrizione(i){
d = mioIframe.document;
switch (i) 
{ 
   case 1 : 
      d.write ("Flights to Chicago: Saturdays."); 
      break; 
   case 2 : 
      d.write ("Flights to London: Fridays."); 
      break; 
   case 3 : 
      d.write ("Flights to San Francisco: Wednesdays."); 
      break; 
   default : 
      d.write ("Sorry, there are no flights"); 
} 
d.close()
}
</script>
...
blablabla <span onmouseover=descrizione(1)>parola1</span> 
blablabla <span onmouseover=descrizione(2)>parola2</span> 
blablabla <span onmouseover=descrizione(3)>parola3</span> 
blablabla 

<iframe name=mioIframe></iframe>
ciao