I am aspiring to becoming a professional landscape photographer and am thinking of purchasing a wide angle lense for the Canon EOS 300D. At the moment with my standard lense im getting to much ground and to much sky in landscape photograph, I would like to chop the top and bottom off without cropping afterwards.

Is this what wide angle lenses do?

Not really, wide-angle lenses allow for, well, a wider field of view, both from left to right and front to back.