Rubber-band selection effect

[Joe Piskor <jpiskor teleline es>]

Hi all - 
        I would like to identify a rectangular area on a GTkPixmap that I am 
displaying in a viewport. I'd like to drag a rectangle over the pixmap and 
retrieve the coordinates (offsets) of the box corners. I can get them with 
single mouse clicks within the viewport area (defining top-left and 
bottom-right) but I'd really prefer the visual feedback. Soething like the 
Gimp's marching ants would be exceptional, but for now a simple rubber-band 
rectangle would be sufficient.
        I'd appreciate any pointers to shove me in the right direction; I've pored 
over my FM's to no avail. Any help is appreciated.

Thanks...