Launch Visual Studio .Net and from the main menu select "Tools" and "Customize toolbox"

A new window will appear. Select the ".Net Components" tab on the new window.

A list of all the available components will appear, each with a checkbox. If the component is checked it will appear in your toolbox.
If your desired components are not listed in this list, choose browse.

A standard browse dialog will appear. Now find your assembly (the.DLL file containing the controls). Select it and press "OK".

The assembly's controls will be added to the list. Make sure their checkboxes are checked. Then press "OK".

Your controls should now be available in the toolbox.