This is something that should be so easy as downloading the skins themselves is easy as pie. I have found a very simple method of completing this.
First of all you need the skin itself. It can be found on several places, but most notably on the uTorrent site itself. Go there and find yourself a nice looking skin, and make sure it’s called toolbar.bmp when downloaded!
Open up an Explorer window (or simply open up My Documents or any other folder) and type %AppData%uTorrent in the adress bar. Paste the toolbar.bmp file here!
The only thing you need to do is restart (or open) uTorrent and voila! Your new skin is there!
Have fun, and comment if you find any good skins out there!