This works both for IE and NS and any version of Acrobat :)
Hope it helps someone!

the problem with the other scripts is that it doesn't work for Acrobat 7.0 as the type changed from PDF.PdfCtrl.version to AcroPDF.PDF.1

this code corrects that problem!

feedback appreciated!

var acrobat=new Object();

acrobat.installed=false;
acrobat.version='0.0';

if (navigator.plugins && navigator.plugins.length)
{
for (x=0; x {
if (navigator.plugins[x].description.indexOf('Adobe Acrobat') != -1)
{
acrobat.version=parseFloat(navigator.plugins[x].description.split('Version ')[1]);

if (acrobat.version.toString().length == 1) acrobat.version+='.0';

acrobat.installed=true;
break;
}
}
}
else if (window.ActiveXObject)
{
for (x=2; x<10; x++)
{
try
{
oAcro=eval("new ActiveXObject('PDF.PdfCtrl."+x+"');");
if (oAcro)
{
acrobat.installed=true;
acrobat.version=x+'.0';
}
}
catch(e) {}
}

try
{
oAcro4=new ActiveXObject('PDF.PdfCtrl.1');
if (oAcro4)
{
acrobat.installed=true;
acrobat.version='4.0';
}
}
catch(e) {}

try
{
oAcro7=new ActiveXObject('AcroPDF.PDF.1');
if (oAcro7)
{
acrobat.installed=true;
acrobat.version='7.0';
}
}
catch(e) {}

}