Selecting polygons from raster map using a mouse...CAN IT BE DONE???

[taku at cats.ucsc.edu]

        I am interested in outlining and selecting polygons on raster maps
displayed on screen.  I want to be able to outline them with a mouse and 
then save them as a new raster layer.
        if anyone has done this before or has experience mantling topography
with "blanket" surfaces, please help me out.

                                                Cheers,
                                                        Max Kaufman, UCSC