Why not use the solpart menu for linking pages within your portal or another module like HouseMenu to link between pages.... 

And once you get your site moved over you only need to have the following to link your images....td style="background-image: url('../images/DNN_Xls/portal-shadow_top.png');  It sounds like you may be getting confused on how the url's are being created when in a development and production environment.  Are you trying to build a skin?  Or you adding content to a page?  If using a module to add images, there's no way that I know of getting away from that long url.  If you are building a skin, then once you move your images over to the production environment you can shorten up the url.

Hope this helps

Jerry