Recording Video From one PC to Another I'm planning on recording PC screens in general, including gaming and videos.

I'm aware of screen capture software like FRAPS, Playclaw etc. and have tested them out, but the increased strain on my computer is noticeable while they are active, even with extra background programs closed. 

I'd read elsewhere  about a lag-free solution that sent the video to a second computer running the screen capture software, offloading the extra effort to the second machine and keeping gameplay smooth.

If I intend to try this solution, what hardware and software am I likely to need in order to duplicate the video output and be able to record it with a second machine? Audio recording won't be a problem, as I intend to do that separately.
In order to duplicate the display you would need extra hardware in your machine anyway, otherwise you will still get lag, so I would instead recommend simply upgrading your existing machine - it will be cheaper, and the spinoff is that you will have a better machine.

The machine I am currently writing on has a reasonable GeForce graphics card, quad core i5 and 8Gb of RAM - pretty cheap, but can happily use FRAPS on full screen (1600x1050) at >25 fps while playinng COD4 or MW2 for example.