Get a card that has a proper video output, or go on the cheap and get a realmagic card or something like that so that you can compile a file and watch it on your TV.
First things first though, calibrate your monitor and your TV with some test patterns at least.
The calibrate your capture system to make sure you are capturing the full dynamic range of your source. (ie. that it is no too bright with blown out whites or too dark with crushed blacks)
If the source is still to bright, then set new black and white points.