Originally Posted by Matt555

Ahh, maybe try using a Hue / Saturation Adjustment Layer, in your layers palette click the icon that looks like a circle split into two halves (diagonally) and then select Hue / Saturation, moce the saturation slider all the way to the left to desaturate the layer(s) below it, you can then merge that adjustment layer down to the original layer to permentally desaturate it if you want.

Hope that helps a bit