dipende da cosa devi farci,
questo copre (spero) tutto, prova a semplificarlo se non ti serve così completo
Codice PHP:
<html>
<head>
<title>salva form in cookie</title>
<script type="text/javascript" language="JavaScript">
<!--
var sep='<|>' // separatore

/***************************************\
  funzioni generiche setta/leggi cookie
\***************************************/

function setCk(nome, valore, giorni) {
  var date = new Date(); 
  date.setTime(date.getTime()+(giorni*24*60*60*1000));
  document.cookie = nome+'='+valore+'; expires='+date.toGMTString()+'; path=/';
}

function getCk(nome) {
  var nameEQ = nome + '=';
  var ca = document.cookie.split(';');
  for(var i=0;i < ca.length;i++) {
    var c = ca[i];
    while (c.charAt(0)==' ') c = c.substring(1,c.length);
    if (c.indexOf(nameEQ) == 0) return c.substring(nameEQ.length,c.length);
  }
  return null;
}

/***************************************\
  funzioni salva/setta stato campi form 
\***************************************/

function salva(){
    var f=document.modulo
    var str=''
    for(var k=0;k<f.elements.length;k++){
        var c=f.elements[k]
        if(c.type=='text' || c.type=='textarea' || c.type=='password') str+=c.value
        else if(c.type=='checkbox' || c.type=='radio') str+=((c.checked)?1:0)
        else if(c.type=='select-one') str+=c.selectedIndex
        else if(c.type=='select-multiple') {
            for(var q=0;q<c.options.length;q++){
                str+=((c.options[q].selected)?1:0)+((q!=c.options.length-1)?'|':'')
            }
        }
        else str+=sep // "file", "button", "submit" e "reset" da non settare
        if(k!=f.elements.length-1)str+=sep
    }
    setCk('str',str,365)
}

function setta(){
    if(getCk('str')){
        var f=document.modulo
        var str=getCk('str').split(sep)
        for(var k=0;k<f.elements.length;k++){
            var c=f.elements[k]
            if(c.type=='text' || c.type=='textarea' || c.type=='password') c.value=str[k]
            else if(c.type=='checkbox' || c.type=='radio') c.checked=parseInt(str[k])
            else if(c.type=='select-one') c.selectedIndex=str[k]
            else if(c.type=='select-multiple') {
                var p=str[k].split('|')
                for(var q=0;q<c.options.length;q++){
                    c.options[q].selected=parseInt(p[q])
                }
            }
        }
    }
}
window.onload=setta
//-->
</script>
</head>
<body>
<form name="modulo" onsubmit="if(this.salva_in_cookie.checked){salva()}">
<input type="text">

<input type="password">

<textarea></textarea>

<input type="checkbox">

<input type="radio" name="a">
<input type="radio" name="a">

<select>
<option>0</option>
<option>1</option>
<option>2</option>
</select>

<select multiple="multiple">

<option>0</option>
<option>1</option>
<option>2</option>
</select>

<input type="file">
<hr />
<input type="checkbox" name="salva_in_cookie"> salva in cookie
<hr />
<input type="submit">
</form>
</body>
</html> 
ciao