the first part is easy, you just need to edit you skin to have the text e.g. the default gravity skin has markup such as :

            <div id="search" class="span3 pull-right">

                <dnn:SEARCH ID="dnnSearch" runat="server" ShowSite="false" ShowWeb="false" EnableTheming="true" Submit="Search" CssClass="SearchButton" />

            </div>

You would just add text before the dnn:search tag.

As to the 2nd, there isn't a way with the default search tag - probably the easiest way to do so would be via some jquery/javascript to add text to the search textbox when the skin is displayed. Alternatively clone the search skin object (e.g. admin/skins/search.ascx and search.ascx.cs, rename them and add whatever functionality you require. Finally update the skin to use your new skin object.