I know that some people have been trying to get a clear dock in Leopard and after some playing around I've managed it. Totally clear. You need to download Mirage, unzip it and run the enclosed file. Just leave the top two boxes ticked and click Install (you'll need to authenticate). Your dock will flash and you'll be left with a clear 2D dock. It will however have the original blue dot markers underneath. I much prefer the subtle triangles so if you want to change yours to be the same triangle, download this file, open Finder and go to /Library/CoreServices, right click on Dock and Show Package Contents. A new Finder window will open, click on Contents and then Resources and dump the files within indicators.zip into it. You will need to authenticate as it's overwriting existing files. Open a Terminal windows and type "killall Dock" (case sensitive), your dock will flash again and you'll have the new triangle indicators. If you want to revert, just run Mirage again and click on the Restore gear at the top, make sure all the boxes are ticked and hit Restore.