Convert image to vector

Hi guys,

Yet another challenging task. I will be using a real photo and have to turn into a vector base blakc and grey tone similar to the attached photo.

I have found a few method which is to posterize the image so as to get the different tones and then drawing them over.

Does anyone else have similar experience? What is the best and most effective way to do this?

Will be using adobe CS4 fyi.