RE: Full-screen, computer video capture software
I think the limiting factor is the device you use to capture the video.
USB devices are comparatively slow and therefore would not produce a good looking large screen video. Firewire is a lot faster but I don't know of a device that will capture an analog video signal in real time and display it on your PC.
What ever you end up going with, it's worth considering a solution that writes directly to video memory... this will help minimize the impact of a slower CPU.
Regards,
Bill