This is my starting image. I opened this in photoshop, you can do this in any version of photoshop, but the version i'm using is adobe cs4

The first i thing i did after opening the image in photoshop, was up the top i went to Image > Adjustments > desaturate. which just removes all the colour from your image and turns it black and white.

Then you go to Image > Adjustments > Curves, this tool helps the exposure of the image, but in this case it gives more definite black and whites instead of the image being so grey.

In this image you can see the before (just after it was desaturated) with the curves tool opened, and you can see how grey the image looks.

On the side you can see i've moved the lines, you don't have to do it the same as I did, you're welcome to play around til the image suits your personal taste.
But in this instance this is how I did it.
And already you can see the dramatic change it has made to the image.

This step is optional, this is just something i personally like to do with some of my black and white images.

Go to Filter > Distort > Lens Correction.

Where the red line is where i played around, you can again like i said move this bar to what suits your personal taste, this tool gives a dark edge around your image, and makes the subject in the middle stand out more.

This is what the image looks like with the dark edge.

This is something I do with some of my images, Canon cameras can sometimes produce unsharp images, so I like to sharpen up my image a bit, So i went to Filter > Sharpen > Smart Sharpen

Where the red circle is where i moved the bar, now I only did 2.0 do not do it to intense you want your photo to look as natural and unphotoshopped as you can.

And my final image! A more effective and dramatic and non ametuer black and white, this is how the professionals do it :)