Understand that a video capture device is NOT the same thing as a tuner card. Although a tuner card can be used as a capture device, a capture device cannot be used as a tuner.
If you are coming off your Direct TV box, and will not be needing the tuner feature, you can get by with just a capture device. I am afraid I have not done anything with capture or tuner devices in a few years. Then Hauppauge and ATI were pretty much the only players but now there are dozens so I am not any help in selecting a device.
My recommendation is to first determine the outputs your Direct TV device supports, then go from there, making sure any device you are considering supports Windows 7 - particularly important if running 64-bit Windows 7. While not necessary, and no guarantee, selecting a Windows Logo'd Product
helps minimizing compatibility issues. When you find a capture device you are interested in, plug the brand, model number and the word review
in your favorite search engine and read what is being said about that device.