ah,,time to get out of my spying mode ...been along time since I wrote anything ....okay here goes...
You are more or less on the right track. Or I should say with the right program to do it. The general "convert" to grey is "passable"
But if you really want to do abit more, try going to the menu bar of photoshop and select Image...then adjustment...and then select "channel mixer". Make sure you have a sample picture already opend before you do this.
Okay, you see that little square that says "monochrome" well...click that and you find it changed your picture in the background to black and white. Well in a way it is black and white or grey as you would want to call it. But in reality it still retains it's colour data quality. Now try to experiment with the colour bars. Usually you can't have the sliders all slided to the right or left at the same time...you will be increasing so much brightness to the picture it will be a wash-out effect or vise visa.
Okay in a nutshell, what the slider is trying to do is change the image quality or constrast on various element in the photo. As each slider represent a colour hue, sliding it, you can change the tone or intensity of certain primary colour and that translates into how grey is effected..it could mean...for example..making the sky look bright white, light grey or even dark or black. You can make a person's skin tone from light to dark...etc. Just play around with it and you will see what you can get out of your pictures. Once you master this small bit you will never touch that "convert to grey" option again Sound abit confusing and I am abit rusty with describing it but well..play around with it abit and you get the picture. ( no pun intended eheh)
This function is almost like when photographers shooting film would use colour filters on their lens to capture scene. The colour filter's effect on black and white negative is that it brings up or brings down certain colour range to make the picture look better ( or worst if you are not careful)