Desabilitar submit sino hay ningun checkbox seleccionado

[KarlanKas]

Prueba esto en vez de tu código:

Código HTML:

<script>

function pepe(valor){
	f=document.forms['formul'];
	valor2=true;
	todos=0;
	todos2=0;

	for(a=0;a<f.elements.length;a++){
		if(f.elements[a].type=="checkbox"){
			todos+=1;
			if(valor!=undefined){
				f.elements[a].checked=valor;
				valor2=(valor)?false:true;

			}
			else{
				if(f.elements[a].checked==true){
					todos2+=1
					valor2=false;
				}
			}
		}
	}
	f.elements['enviar'].disabled=valor2;
	f.elements['guardar'].disabled=valor2;
	f.elements['eliminar'].disabled=valor2;
}
</script>

<form name="formul" action="loquesea.php">
<input type="checkbox" id="0" name="seleccion" value="" onclick="pepe(this.checked)" />Marcar Todas<br>
<input type="checkbox" id="1" name="fichier0" value="11" onclick="pepe()" /><br>
<input type="checkbox" id="1" name="fichier1" value="algo" onclick="pepe()" /><br>
<input type="checkbox" id="1" name="fichier2" value="fotos" onclick="pepe()" /><br>
<input type="checkbox" id="1" name="fichier3" value="mariscos" onclick="pepe()" /><br>
<input class="btn" type="submit" id="enviar" name="action" value="enviar>" disabled="disabled" />
<input class="btn" type="submit" id="guardar" name="action"  value="guardar" disabled="disabled" />
<input class="btn" type="submit" id="eliminar" name="action"  value="eliminar" disabled="disabled" />
</form>