Ciao e grazie! Ti allego il codice della pagine per rendere più chiara la situazione.
codice:
  
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>ART</title>
<script type="text/javascript">
<!--
function MM_findObj(n, d) { //v4.01
  var p,i,x;  if(!d) d=document; if((p=n.indexOf("?"))>0&&parent.frames.length) {
    d=parent.frames[n.substring(p+1)].document; n=n.substring(0,p);}
  if(!(x=d[n])&&d.all) x=d.all[n]; for (i=0;!x&&i<d.forms.length;i++) x=d.forms[i][n];
  for(i=0;!x&&d.layers&&i<d.layers.length;i++) x=MM_findObj(n,d.layers[i].document);
  if(!x && d.getElementById) x=d.getElementById(n); return x;
}
function MM_preloadImages() { //v3.0
  var d=document; if(d.images){ if(!d.MM_p) d.MM_p=new Array();
    var i,j=d.MM_p.length,a=MM_preloadImages.arguments; for(i=0; i<a.length; i++)
    if (a[i].indexOf("#")!=0){ d.MM_p[j]=new Image; d.MM_p[j++].src=a[i];}}
}
function MM_swapImgRestore() { //v3.0
  var i,x,a=document.MM_sr; for(i=0;a&&i<a.length&&(x=a[i])&&x.oSrc;i++) x.src=x.oSrc;
}
function MM_swapImage() { //v3.0
  var i,j=0,x,a=MM_swapImage.arguments; document.MM_sr=new Array; for(i=0;i<(a.length-2);i+=3)
   if ((x=MM_findObj(a[i]))!=null){document.MM_sr[j++]=x; if(!x.oSrc) x.oSrc=x.src; x.src=a[i+2];}
}
//-->
</script>
<style type="text/css">
<!--
body {
	background-color: #000;
}
-->
</style></head>

<body onload="MM_preloadImages('jaib.gif','secretb.gif','avalonb.gif','lavoisierb.gif','doppio-sognoB.gif','humanlandscapesb.gif','advb.gif','contactb2.gif','publicationsb.gif','archivesb.gif','sunflowerb.gif','syncretismb.gif', 'landscapesb.gif', 'videob.gif','molecoleb.gif','whiteb.gif','cementb.gif')">
<table width="28%" border="0" align="right">
  <tr>
    <td width="100%">[img]logo_GA_oro_neg_flash.jpg[/img]</td>
  </tr>
  <tr>
    <td>[img]heart.gif[/img]</td>
  </tr>
  <tr>
    <td>[img]jai.gif[/img]</td>
  </tr>
  <tr>
    <td>[img]cement.gif[/img]</td>
  </tr>
  <tr>
    <td>[img]white.gif[/img]</td>
  </tr>
  <tr>
    <td>[img]molecole.gif[/img]</td>
  </tr>
  <tr>
    <td>[img]syncretism.gif[/img]</td>
  </tr>
  <tr>
    <td>[img]sunflower.gif[/img]</td>
  </tr>
  <tr>
    <td>[img]humanlandscapes.gif[/img]</tr>
  <tr>
    <td>[img]doppio-sogno.gif[/img]</td>
  </tr>
  <tr>
    <td>[img]lavoisier.gif[/img]</td>
  </tr>
  <tr>
    <td>[img]avalon.gif[/img]</td>
  </tr>
  <tr>
    <td>[img]secret.gif[/img]</td>
  </tr>
  <tr>
    <td>[img]landscapes.gif[/img]</td>
  </tr>
  <tr>
    <td>[img]archives.gif[/img]</td>
  </tr>
  <tr>
    <td>[img]publications.gif[/img]</td>
  </tr>
  <tr>
    <td>[img]contactB.gif[/img]</td>
  </tr>
  <tr>
    <td>[img]video.gif[/img]</td>
  </tr>
  <tr>
    <td>[img]property.gif[/img]</td>
  </tr>
  <tr>
    <td>[img]adv.gif[/img]</td>
  </tr>
</table>
<map name="Map" id="Map">
  <area shape="rect" coords="20,1,172,11" href="human.html" target="mainFrame" />
</map>

<map name="Map2" id="Map2">
  <area shape="rect" coords="36,2,166,11" href="doppiosogno.html" target="mainFrame" />
</map>

<map name="Map3" id="Map3">
  <area shape="rect" coords="60,1,145,11" href="lavoisier.html" target="mainFrame" />
</map>

<map name="Map4" id="Map4">
  <area shape="rect" coords="57,1,140,12" href="avalon.html" target="mainFrame" />
</map>

<map name="Map5" id="Map5">
  <area shape="rect" coords="55,0,147,11" href="secret.html" target="mainFrame" />
</map>

<map name="Map6" id="Map6">
  <area shape="rect" coords="47,1,157,11" href="dreamography.html" target="mainFrame" />
</map>

<map name="Map7" id="Map7">
  <area shape="rect" coords="51,0,147,11" href="landscapes.html" target="mainFrame" />
</map>

<map name="Map8" id="Map8">
  <area shape="rect" coords="48,1,148,11" href="archives.html" target="mainFrame" />
</map>

<map name="Map9" id="Map9">
  <area shape="rect" coords="2,2,198,198" href="index.html" target="_parent" />
</map>

<map name="Map10" id="Map10">
  <area shape="rect" coords="43,2,149,11" href="publications.html" target="mainFrame" />
</map>

<map name="Map11" id="Map11">
  <area shape="rect" coords="43,1,152,11" href="contact2.html" target="mainFrame" />
</map>

<map name="Map12" id="Map12">
  <area shape="rect" coords="20,1,182,12" href="home.html" target="_parent" />
</map>
<body leftmargin="0" topmargin="0">
</body>
</html>

Naturalmente avrei preferito utilizzare un codice html come già ho fatto ma effettivamente sono agli inizi e non vorrei complicarmi troppo la vita.
I pulsanti si "trovano" nel leftframe e caricano una pagina Htlm nel mainFrame.
Come noterai c'è già onmouseover e onmouseout che carica due gif diverse (cambia la luminosità del tasto quando ci passi sopra il mouse). In questo codice dovrei inserire lo spegnimento dei pulsanti? per ogni singolo pulsante dovrei ripetere la procedura così come ho fatto con il onmouseover? Infine dovrei creare un terzo gif per il pulsante "spento"?
Grazie ancora.

Giovanni