Creating a Query and then a select box based off query results


I am a newbie here and was hoping someone had some experience and
suggestions on how to accomplish the below task:

I would like to figure out how to give my users a prepopulated list
based off there selection. I am creating am application that users
specific servers and would like to show them the list of suppliers who
build these servers. For example, if they chose a server X200 the
next box would then prepopulate its self with the supplier thats is
responsible for building this server. Anyone have any idea how I would
go about doing this. I have a query that pulls the data but I have no
idea what my next steps should be.

Thank You,

Roughly you will change the view when the user selects a server.
Use the onchange (not onclick) event of the select box
to trigger the next view.
Obviously that should be an Ajax call, since there is no
need to update the whole page.

something similar, a category select with subcategories:

the view with the main category select:

<select name="category_main" id="category_main" style="float:left;
width:200px;" onchange="<%= remote_function(:url =>
sub_category_depot_product_url(@product), :with => "'category_id=' +
this.value") %>">
           <option value='666'>Kies een categorie</option>
          <%= options_from_collection_for_select(@categories, "id",
"title", (@product.category ? @product.category.category_id : 0)) %>

the action to get the sub categories:

  def sub_category
    @product = Product.find(params[:id])
    @categories = Category.find(:all, :order => "title
ASC", :conditions => "category_id = #{params[:category_id]} AND
    respond_to do |format|

the ajax response used by this action:

page.replace(:category_sub, :partial => 'depot/products/
sub_category_select', :locals => {:categories => @categories, :product
=> @product})

and the partial used by the ajax response:

<select name="product[category_id]" id="category_sub"
style="float:left; width:200px; margin-left:8px;">
  <%= options_from_collection_for_select(categories, "id", "title",
product.category_id) %>

Thanks, this pretty helpful. I am going through this step by step. Had no idea even how to begin this or even what to call it when try to find a solution