Depends on what parts you want to be transparent.
There's add on to nUI that hides the top console artwork, and some skins hide it as well, only leaving the buttons and the latency/fps counters visible.
If you want to make the dashboard itself transparent then only the upper part could be made transparent, as the larger part is just empty space below the art.
To explain it a bit better;
http://www.wowinterface.com/download...nUILovely.html