risolto...

codice:
<script language="Javascript">

function verifica(campo)
{
var chiffres = new RegExp("[0-9]"); 
var verif;
var points = 0; 

for(x = 0; x < campo.value.length; x++)
{
verif = chiffres.test(campo.value.charAt(x));
if(campo.value.charAt(x) == "."){points++;} 
if(points > 1){verif = false; points = 1;} 
if(verif == false){campo.value = campo.value.substr(0,x) + campo.value.substr(x+1,campo.value.length-x+1); x--;}
}

}
</script>

<script  type="text/javascript">
 function conta(val) {
	var max=10
        if (val.valore.value.length > max) {
        val.valore.value = val.valore.value.substring(0,max)
        } 
	
	
        
 }
 
</script>
<input type="text" name="valore" size="44" onkeyup="conta(this.form);verifica(this);"/>



Ciao e grazie comunque