The desired effect can be achieved easily with CSS and this approach will even allow for finer tuning of the desired effect.

The RadWindpw's ContentTemplate is a simple div element that has dimensions set in pixels by the RadWindow scripts, so you can control the way its contents flow just like any other generic div element on your page. Below follows an example.

In case an external page is loaded in the RadWindow (e.g., via the NavigateUrl property), it will be loaded with an iframe that has its width and height set to 100% of the RadWIndow content area. Thus, it is up to the content page to control its scrolling.

<%--A sample RadWindow declaration you can use for quick testing--%>
<telerik:RadWindow ID="RadWindow1" runat="server" VisibleOnPageLoad="true">
	<ContentTemplate>
		<div class="desiredOverflow">
			Add your content here
			<div style="height: 1000px; width: 1000px; background-color: yellow;">
				some dummy content so you can test out the overflow CSS rules behavior
			</div>
		</div>
	</ContentTemplate>
</telerik:RadWindow>


/* some sample CSS that you can use to control the scrolling behavior of your content */
.desiredOverflow
{
	width: 100%;
	height: 100%;
	margin: 0;
	padding: 0;
	overflow: scroll; /* set the desired value here */
	/* you can also use the other overflow rules for fine control */
	overflow-x: hidden; /* set the desired value here */
	overflow-y: scroll; /* set the desired value here */
}