The ID forum is your friend.
Moving this discussion to the InDesign forum.
Are you trying to convert just selected content to grayscale, or the entire document?
The entire document can be converted by exporting to PDF (Print), choosing Convert to Destination under Color Conversion in the output section, then choosing a grayscale profile for the destination. If you have distiller, or the AdobePDF virtual Printer installed yolu acan also print to file or directly to PDF choosing Composite Gray as the destination space, but export is the preferred method in CS6 (grayscale export is not available in earlier versions).