I already answered your support ticket on the subject. For convenience I will paste my answer here as well.
Could you please specify which scrollbars you are referring to? Using its default settings, RadEditor displays vertical scrollbar in its content area when the content exceed the size of the viewport.
In addition, if AutoResizeHeight property is set to true the RadEditor will extend its height when the content exceed the initial size.
In addition, the version that you are currently using the quite old and it is highly recommended to use latest version of RadControls for ASP.NET AJAX (currently 2011.2.712). For example modern browsers like Internet Explorer 8, Internet Explorer 9, Firefox 3+, etc. are not supported by the used version.
All the best,
the Telerik team