Hi Mark,
Yes there is an easy way its just a gap in documentation.
You can add an image from the skin folder to layout.master like this:
<portal:SkinFolderImage ID="imgs1" runat="server" ImageFileName="sun5.gif" CssClass="sunheader" />
so you only have to put the image file name and it will resolve the rest of the url correctly.
Hope it helps,
Joe