VSTO 2005 does not create a "shared add-in", it creates a VSTO add-in. A "shared add-in" is something else and is not supported in the VSTO forum.
There's no way for you to directly "convert" an XML file to a command bar; not in Office and not in VSTO. Basically, all you can do is work through the XML file logically, and create the toolbar/menu based on the information it contains. But you have to work out the logic and code yourself.
Since we have no idea how the logic of your XML file is built or how your menu should look, there's simply no way we can offer anything more concrete. If you don't know how to read an XML file using VS 2005's XML tools, then please ask in a forum that supports the .NET Framework XML namespaces.
Cindy Meister, VSTO/Word MVP