Ciao Dr Mal,

intendi una cosa tipo questa?
codice:
<form name="NomeForm">
  <input type="checkbox" name="chk1" value="1">

  <input type="checkbox" name="chk2" value="1" onclick="if(this.checked)this.form.chk1.checked=true">

  <input type="checkbox" name="chk3" value="1" onclick="if(this.checked)this.form.chk1.checked=true">

  <input type="checkbox" name="chk4" value="1" onclick="if(this.checked)this.form.chk1.checked=true">

</form>