How to Colorize B/W Photo Digital Images

Hi, seems like a daft question, but let me explain slightly more.

What I need to do is to be able to take a black and white (and greys of course) digital picture and assign each part of the grey scale a different color. I could cut down the resolution to say either 8 or 16 bit to make it a bit easier, even 8 different colors would be OK, but 16 would be super........

What I need is to be able to assign colors myself to each level and then to make them visible in the picture and save it on my PC with the added color.....

This has NOTHING to do with making skin looking like skin or grass green again......its just assigning a particular level of gray to a specific color, and then coloring in the picture.....even if the person photographed looks most odd at the end of the day....that does not matter and is completely unimportant.

If I can do it with freeware like Paint or Gimp, or in Corel Draw 11 (as I just happen to have a copy of that), I would be most gratefull....

Hopefully that makes sense to some of you at least....

If I haven't stated my case very clearly, please ask me questions and I will do my best to answer them accurately!!!