Does the print screen button work from within a FiveWin program? I imagine it does. If so, I wonder would it be possible to put the right key code into the keyboard buffer - probably wouldn't work but it might be worthwhile attempting.
There are utilities that do this under windows - both freeware and stuff you have to pay for - that you could shell out to using RUN command or WinExec() function or something. Some may still operate off PrintScreen button but some of the free ones come with source code. See:
http://graphicssoft.about.com/od/screen ... indows.htm
So you should be able to modify them to run off a command line.
Linux, of course, includes a specific program for doing this (gnome-screenshot) that you can run from the menu or via PrintScreen key or other configurable key combination or include on any panel but I guess that doesn't help you.
Good luck
xProgrammer