Checkbox and Textbox validation

Please advise as I would like to make sure a textbox is populated if a Checkbox is selected.

My Checkbox has two selections with one already checked:

Account<input TYPE="Radio" name="account" value="Yes" CHECKED />Yes
<input TYPE="Radio" name="account" value="No" />No
<br>
Names<TEXTAREA COLS="12" ROWS="3" NAME="names" WRAP="soft"></TEXTAREA>


Now I need to make sure if it is checked "Yes" then a message will come up if the "Names" Box is blank.
If the checkbox is checked with a "No" and the "Names" box is populated then I need an alert message saying the "No" checkbox should not be checked if the "Names" field is populated.


My attempt:


var checked;

if(document.myformnamehere.account.checked.value == "Yes")
{
checked = true;
if(document.myformnamehere.names.value == "")
{
alert("names needs to be populated if account request is checked with yes");
return false;
}

}
else if(document.myformnamehere.account.checked.value == "No")
{
checked = true;
if(document.myformnamehere.names.value != "")
{
alert("names can not be populated if account request is checked with no");
return false;
}

}

<script language="JavaScript">
function vd(){
var strAlert='';
//loop through the collection of radio buttons
for (i=0;i<document.f1.account.length;i++){
// if we find one that's checked
if (document.f1.account[i].checked){
//return its value
strAccount=document.f1.account[i].value;
}
}

switch(strAccount){
case 'Yes':
if (document.f1.names.value==''){
strAlert='names needs to be populated';
}
break;
case 'No':
if (document.f1.names.value!=''){
strAlert='names cannot be populated';
}
break;
default:
strAlert='You have broken our form'
}
if (strAlert!=''){
alert(strAlert);
}
}
</script>


Any use?