Picking with multiple viewports

In this application i’m writing, I use a standard 4-view modeling interface. The perspective view is the largest, and the three 2D-views are of equal size. I’d like to constrain proportions, so the aspect ratios for these views are important. Thus I set up one ortho (and viewport) for each of the 2D views. And here comes the problem: I’d like to pick the vertices drawn in 2D-views and move them around. But I don’t know how to convert the coordinates of a vertex from one view to mouse- or screencoordinates, nor the other way around. How do you do it? it would really help me out now…

anyone? thanx in advance