Something

          <select name="file.Game.GameID" id="file.Game.GameID">
            <option value="0" selected>Select a Game</option>
            #foreach($item in $games)
            <option value="$item.GameID" #if($game.GameID == $item.GameID)selected#end>$item.Name</option>
            #end
          </select>
          <br />
          <br />
          <span id="category">
            #parse("file/fetchcategories.vm")
          </span>
          <script type="text/javascript">new Form.Element.Observer($("file.Game.GameID"), 1, function(element, value) { new Ajax.Updater('category', 'fetchcategories.aspx', {asynchronous:true, evalScripts:true, parameters:'value='+value}) })</script>
          <span id="brand">
            #parse("file/fetchbrands.vm")
          </span>
          <script type="text/javascript">new Form.Element.Observer($("file.Category.CategoryID"), 1, function(element, value) { new Ajax.Updater('brand', 'fetchbrands.aspx', {asynchronous:true, evalScripts:true, parameters:'value='+value}) })</script>