You didn't specify if you are using an external page as content (i.e. NavigateUrl is set) or you use RadWindow as controls container. In both cases however, RadWindow does not control the scrollbars in any way. Basically, when an external page is used RadWindow uses an IFRAME and the scrollbars come from the IFRAME itself. When RadWindow is used as a container, the scrollbars are shown inside the container.
This being said, I would suggest to use CSS and apply overflow property to the container in order to avoid the scrollbars. As for showing RadWindow from the server, you need to set its VisibleOnPageLoad property to true.
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