form validation using RJS

Hi
I have a form as below

<%= form_remote_tag :update => "update_sd_resolution_ui",
                    :url => { :action => 'sd_resolution_save',
                               :id => @sd_ticket.id,
:sd_resolution_id=>@sd_resolution_id},
                               :class => 'itilform'%>

<table>
<th width=""><label for="" >Hr: </label></th>
    <td><%= text_field :sd_resol, "hours", "size" => 2 %></td>
</table

<%= end_form_tag %>

HERE HOW CAN I CHECK Hr field contains only numbers .How can i implement
this using RJS.Say forexample can i call a javascript function for form
checking from
form_remote_tag above?

Sijo