HOW TO
In earlier versions of ArcMap, such as version 9.3.1, it was possible to dock toolbars vertically between the Table of Contents and the Data Frame, a shown in the image below.
On ArcMap versions 10.x, this capability was no longer available. This is a known limitation. Newer versions of the software use the new dockable window framework which prevents docking toolbars between the TOC and the data view.
Get help from ArcGIS experts
Download the Esri Support App