You will need to have Skin Studio 7 to edit the file. It was not designed to work properly with the small tool bar or that is icons.

I made a substyle for the small icons and called it just that Diamond Small icons and then made my adjustments to the skin to have it work correctly. As seen here...

Then the adjustment was done to the tray section with a -negitive number being used for the top section in the text settings as seen here...

thus you get this results with your skin as seen here...

Those black areas usually happen due to a transparency setting being used in wb7 for this type of skin. [Which is designed to not use trans. settings.] There are several ways to correct the issue. But the easiest way is to open up wb7 and change the transparency setting to the reset all link at the bottom right side below Vista-ize me link. Then reapply the skin with those settings. The skin itself has trans. and the level if trans made into the images and how it is setup in the skin itself. Using diamond as your model skin to start a wb with is ok. But has it's draw backs with some of these things present to be changed so as it to work correctly with trans settings.

You can try checking into the wiki pages for wb's to figure the rest of the trans settings for each elements changes for it to work properly with these settings.

Wiki is here at this link WC Wiki