> Are there devices that can capture a VGA signal.

There are, but very expensive... If anything you're better off using TV-in for captures.

> For example, I have a VGA
> box for my xbox and would like to take screenshots from games.

If you can run modified code, there should be a way of doing that already...

> I am looking for
> a device that would capture the VGA signal much like a video capture card can
> capture an NTSC signal.

Sorry, I tried looking for one but could not find such a thing on sale online