you could try googleSketchUp which is for free. it's a very basic CAD app. realitivly easy to use. better is the full version of sketchUp5, you could use the trail version from their site for 30 days free usage. unfree:
i find vector works is good for 2d (floor plans). a very grafic orientated app. archicad is good espacially for 3d but not easy to use.