Puoi fare cosi...
codice:
<HTML>
<HEAD>
<SCRIPT LANGUAGE="javascript">

function show_hide(anObject) {
   if(document.all) {
      if (anObject.style.visibility=="hidden") {
			 showObj=false;
			} else {
			 showObj=true;
			}
   } else {
      if(document.layers) {
         if (anObject.visibility=="hide") {
			     showObj=false;
			   } else {
			     showObj=true;
			   }				 
      } else { 
         if(document.getElementById) {
            if (anObject.style.visibility=="hidden") {
			        showObj=false;
			      } else {
			        showObj=true;
			      }				
					}		
			} 
   }
	 if (! showObj) {
			 show(anObject);	 
	 } else {
			 hide(anObject);	 
	 }
} // function show_hide(anObject)

function hide(anObject)
   {
   if(document.all)
      anObject.style.visibility="hidden";
   else
      if(document.layers)
         anObject.visibility="hide";
      else
         if(document.getElementById)
            anObject.style.visibility="hidden";
   }

function show(anObject)
   {
   if(document.all)
      anObject.style.visibility="visible";
   else
      if(document.layers)
         anObject.visibility="show";
      else
     if(document.getElementById)
            anObject.style.visibility="visible";
   }
</SCRIPT>
</HEAD>
<BODY>


<DIV ID="pluto" STYLE="position:absolute;top:200;lest:40;">
   <FORM>
	   <input type="checkbox" name="c1" onClick="show_hide(document.getElementById('T1'))"><INPUT TYPE="text" NAME="T1" SIZE="20">
		 

	   <input type="checkbox" name="c2" onClick="show_hide(document.getElementById('T2'))"><INPUT TYPE="text" NAME="T2" SIZE="20">
   </FORM>
</DIV>

</BODY>
</HTML>