Make B&W pictures out of colour jpegs?

Well, for artistic effects, I've been wondering how to make colour jpegs saved on my computer to black and white! And I know everybody says PHOTOSHOP PHOTOSHOP!! NO i am not using photoshop it is too complicated, too expensive and the trial is incrdibly restricted. Can somebody tell me any freeware that can convert colour jpegs to black and white, or tell me techniques with microsoft photo editor?