You're correct.
You MUST perform the Infragistics controls install before installing the MM.NET Infragistics controls.

See the MM.NET Dev Guide's topic "Adding MM .NET Windows Forms Controls to the VS .NET Toolbox" for the detailed steps for adding the controls to the toolbox (changing only step 6 directory to C:\Program Files\Mere Mortals .NET Framework 2003\Third Party Components\Infragistics Windows Controls).