Grazie, ma non va cioè il checkbox rimane non fleggato:

codice:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title>Pagina senza titolo</title>
    
<script language="javascript" type="text/javascript">
// <!CDATA[

function window_onload() 
{
    var p = document.getElementById("personale");
    if(!p) return;
    
    p.ValoreOriginale = "<%="valore originale"%>";
    p.onblur = function()
    {
        document.getElementById("C1").checked = (this.value != this.ValoreOriginale);
    }
    
    
}

// ]]>
</script>
</head>
<body onload="return window_onload()">
    <form id="form1" action="pagina.asp">
        <input id="personale" name="personale" value="<%=objRs("personale")%>" />
        <input type="checkbox" id="C1" name="C1" value="ON" disabled="disabled"/>
    </form>
</body>
</html>