Viewports?

I am trying to put a border around my viewport.. however doing so is proving to be a big tough. I basically have a class that controls it's own viewport, now that class can access it's size and x/y (via getviewport object) but using these as the coords for the boundary isn't correct because those are screen coords not viewport coords. I tried zeroing the VIEW transform matrix, but that didn't work. Anyone have any hints? thanks!