Ok this is a strange effect and i have never seen it before , i encouraged a friend to get OD and since he installed it (on to a fresh install of XP SP2) it has been showing a ghost image of the dock behind it. It is just a normal classic dock and when you hover over an icon it enlarges and you can see a duplicate of the icon behind it (but not zoomed in on) His system is a laptop with Intel Celeron M 1.4GHZ with Intel extreme graphics 512 Ram and a 40 GB HD.
I was thinking that perhaps the onboard graphics just cant cope with the dock but if you close OD then start it again the ghost image is gone but then after a restart its back.