I'm going to guess that submit means he wants to capture digital content from his desktop such as possibly streaming video in a window, a game that is being played, or something like that.
Your idea of running your video card outputs to a capture cards input *could* work, but there are a number of factors working against you there.
First of all, most capture software brings up a window showing what you are capturing. If you see your own capture window on the desktop you'll basically get a video feedback loop (not unlike a microphone picking up sound from a speaker and making a sqealing sound.) The video version is an infinite mirror effect ... I have no idea what kind of adverse effects that could have on your card or the actual capturing. In some capture software you can turn off preview which would avoid this problem, however capture is an intensive real-time process. you will drop tons of frames if not outright freeze up if you try to capture video while doing other things. Also, doing this you'll be capturing an analog signal at 720x480 so you will loose all sharpness and it will be reduce to VHS tape quality essentially.
I haven't had to capture an animated desktop, but I would look around for software that dumps your screen to an AVI file or image sequence (that can later be rendered into a video file) before trying to capture this way. Some type of continuous screen-shot software.
An ugly, but less technically challenging workaround world be to output your desktop to TV and record it with a VCR, then capture from the VCR ... but that would incur visual loss ...
