Dynamic Table Row

I'm playing with rails and RJS,

What I want I think sounds simple - but I can't seem to figure it out.

So basically I have a Countries Model, which joins on Cities Model.

I want to display a list of countries in a select, when you select a
country it shows all the cities in that country.

That works just fine - the issue I have is to add the data in tables.

I have right now a index page

<h1>Listing countries</h1>
<div id="mytable">
<table border="1">
  <tr>
    <td>Please select country</td>
    <td><%= select_tag(:id ,
options_from_collection_for_select(@countries, :id, :country)) %></td>
  </tr>
  <tr>
    <div id="show_cities"></div>
  </tr>
</table>
</div>
<%= observe_field :id, :frequency => 0.25, :url => {:controller =>
"countries", :action => 'show'}, :with => 'id' %>

So when the user chooses a country it gets all the cities of that
country, now all I want to do is add a new row to the existing table,
with a new select containing the cities. My show.rjs does

page.replace_html :show_cities, :partial => 'show', :object => @country

And then the partial is

<td>Please select city</td>
    <td><%= select_tag(:id ,
options_from_collection_for_select(@country.cities, :id, :title))
%></td>

And it displays the data, but not in the exiting table...I know this
probably isn't strictly rails as its javascript/html but maybe someone
can help... All I want is to be able to add new rows when the data is
available?

<h1>Listing countries</h1>
<div id="mytable">
<table border="1">
<tr>
<td>Please select country</td>
<td><%= select_tag(:id ,
options_from_collection_for_select(@countries, :id, :country)) %></td>
</tr>
<tr>
<div id="show_cities"></div>
</tr>
</table>
</div>

Browsers are often a bit finnicky about inserting stuff into tables.
Strictly speaking you shouldn't have a div there - a tr should contain
td tags and things like that. In the past I've also found that
inserting a tbody with some rows to work better than just inserting
rows.

Fred