Q. I want to make part of an image grayscale but keep some color elements.

Answer: There is always more than one way to do something in Photoshop.

#1 Select the area you want to be grayscale. Create a new Hue/Saturation Adjustment Layer (half-moon icon in the Layers palette). Dial down the Saturation.

#2 Make a copy of your image and make it Grayscale.
After creating a layer in the color image with just the part of your image you want to still be color paste the Grayscale image under this layer.

Your image will still be a color image with elements that look grayscale.