It doesn't appear in the list under Graphics Mods? As long as the xml file is there it should be recognized. Are the files inside a folder in the zip file? If so, try zipping the files directly instead.
Mine work perfectly. All the .png named the same as the basic ones, the text file a simple edition of the original (making sure the things between <> are still intact), and the whole thing inside a .zip file just like the basic graphics.
If you manage to get it working, please post pictures.
