Problem solved about appearing and disappearing of Docky, i used the stable PPA of Launchpad. But now i've got some weird issue.
See this link: http://img685.imageshack.us/img685/357/werkblad1001.png
Does anyone know how that black part can be that big and covers at least 20% of my desktop??? Changing settings of Docky has no result what so ever. I'm using 64-bit Ubuntu version 10.04.3.