That's basically how they are going to be. TV resolution is much lower than your PC and it is interlaced.
High quality screenshots released by gaming companies are taken directly from the frame buffers of the machines (Xbox, GC, PS2) and therefore will always look better.
Try playing with your settings a little. I don't know what tuner you bought, but many of them offer several different choices of codecs to use when encoding. Perhaps another might yield greater results.
