Finally i got the solution for the Skin issue in Telerik Rad controls for asp.net Q3,2011.
Skin Issue on reading the post, i came to that the skins for the controls have been moved from Telerik.web.dll to Telerik.web.Ui.Skins.dll. So it is necessary to refer the dll from the
Bin40 of installation folder to the project. The available skins will be available if we close and re-open the project.