Hardware encoding isn't necessary for digital video. The digital data in the digital video is the same kind of digital data that computers love. Digital video is recorded on the hard drive without any encoding or processing.
There are a couple of issues to be addressed by your question about eventually geting digital cable. Without knowing which cable carrier you use, I would not plug it into the svideo in on the tuner card. Svideo is an analog connection, and your tuner card would probably have to convert the digital video signal to analog, and then reconvert it to digital as it gets to you digital panel. Naturally, picture quality will suffer because of the conversion process.
Secondly, much of your cable TV progams will be encrypted, so that you probably will get a black screen from shows on HBO, for instance. I don't think there is any software or hardware that can decrypt premiums cable channels.
What most people do is directly connect the digital HD cable to the LCD or plasma, by passing the computer.
As of right now, the only way that you can legally record satellite and cable HD channels is with the HD recording stuff you get from the carrier. DirecTV and Tivo have stand alone recorders to record HD. I don't know much about recording equipment for HD cable.
However, you can record HD TV from local TV broadcasts with your computer. All over-the-air HD TV is free and unencrypted in the US, for the present. So, that is where your PC's HD tuner will deliver for you.