codice:
<script>
function tutti(obj) {
f = obj.form;
v = obj.checked;
for (i=0;i<f.elements.length;i++) {
  e = f.elements[i];
  if (e.type=="checkbox"&&e.name.substr(0,5)=="campo")
    e.checked = v;
}
}
</script>
...
...
<input type="checkbox" onclick="tutti(this)">
<input type="checkbox" name="campo1">
<input type="checkbox" name="campo2">
...
ciao