gistfile1.js

var list = $$("#yourDataTable tr");
var filter = $('yourFilterField')
list.each(function(elm){
  elm['keys'] = elm.innerHTML.stripTags().toLowerCase();
});
var lastValue = $F(filter);
filter.observe('keyup', function(e) {
  var value = this.value.toLowerCase();
  if (value !== lastValue) {
    list.each(function(elm) {
      if (elm.keys.include(value)) {
        elm.show();
      }else{
        elm.hide();
      }
    })
    lastValue = value;
  }
});