For some reason I was unable to respond to the last question that I posted, dealing with the DVI to HDMI converter cable, so I am just creating a new question.
Anyway, I checked the resolution output from the machine I am trying to do screen captures of, and it produces 1680 x 1050 resolution output, which is not one of the resolutions supported by the PiCapture. Does this simply mean that I cannot use this machine with PiCapture? Or is there a way around it?
You should be able to change the output resolution of your display card to one of the standard resolutions. Here is a link for doing that in Windows:
Change Screen Resolution in Windows
You can tell which supported resolution the PiCapture is recognizing using the 4 green LEDs on the board.