Inkjet printers like RGB so you can sometimes achieve better print results if you convert the image back to RGB after going grayscale - it will still be shades of gray.
Corel Photo-Paint: Image > Convert to... > Grayscale (8-bit)
Adobe Photoshop: Image > Mode > Grayscale
Adobe Photoshop Elements: Image > Mode > Grayscale (say OK when asked "Discard Color Information?")
Jasc Paint Shop Pro: Colors > Grey Scale


