I am not quite sure that I completely understood the dragging problem you describe. I tested our online demos in a few scenarios under IE7 but I was not able to reproduce a problem with the browser scrollbars.
Would you please try to reproduce the problem with our demos
and in case you succeed, send us detailed reproduction instructions? Once we are able to examine the problem, we will offer you a solution in which you should not have to disable the dragging functionality.
In case you want just to hide the drag handler, you can set the RadSlider's ShowDragHandle property to false.
the Telerik team