[Sweet]

<table border="1" cellspacing="0" cellpadding="4">
  <tr><td></td><td></td></tr>
  <tr><td></td><td></td></tr>
</table>
<script>
var cells = document.getElementsByTagName('td'), a = []
for(var i = 0, len = cells.length; i < len; i++){
  a[i] = document.createElement('input')
  a[i].onclick = function(){
    this.value = 'Clicked!'
  }
  cells[i].appendChild(a[i])
}
</script>

Почитай тут. Особенно 4й пункт