I you open up the productlist.ascx page located in your \desktopmodules\smith.buynow folder on line 25 you will see the following code:
<td valign="top" runat="server" id="tdMenuCategories"> <asp:Menu ID="MenuCategories" runat="server" OnMenuItemClick="MenuCategories_MenuItemClick"
BorderColor="GradientActiveCaption" BackColor="White" BorderWidth="1px" Width="107px" Height="151px" BorderStyle="None"></asp:Menu>
</td>
The asp.net control that renders the category menu is an asp:menu and currently its inside a table cell that places it to the left of the products. If you want to move it above the products then create a table row above the products and move the asp:menu control in the new row your create. To make the asp:menu horizontal instead of vertical add the property Orientation="Horizontal" in the asp:menu control.
-Scott