The RadEditorSharePoint.dll and RadEditor.Net2.dll are in the server's GAC. You can also extract them from the solution file (RadEditorMOSS.wsp). Rename this file to .cab (RadEditorMOSS.cab) and open it with Microsoft's cabinet viewer (most archiving software supports .cab files as well). Once you have the two .dll files, you can use them as reference in your VS 2005 project. Note that you do not need to include them in your web part output, since the editor is already installed in the GAC.
All the best,
the Telerik team