Things You'll Need:
Windows XP MCE or Windows Vista/7 Home Premium or above
TV tuner card
Empty PCI slot
1. Turn off your computer and disconnect the cables from the back. Open the side panel of the computer. Usually, it will be attached using Phillips head screws, but occasionally it will have thumb screws which can be opened by hand.
2. Locate an empty PCI slot. They are usually fairly long and off-white colored. Line up your card with the slot and press down gently but firmly. Once the card cannot go down anymore, it is installed. Replace your back panel and reattach all the cables.
3. Attach a cable to your cable box or external antenna and then to your TV card. There are several types of connectors available, including Svideo, RCA, Composite and HDMI. Most commonly, you will be using RCA or Composite cables. They are usually color coded to show you where to install them. Attach the other end of the cable to your TV tuner card.
4. Turn on your computer, click the "Start" button and click "Windows Media Center."
5. Navigate within Media Center to "Settings." Select "TV" and then select "Set up a signal."
6. Follow the onscreen prompts to tell Windows where you live and what kind of signal you are using (ATSC is a high definition signal while NTSC is a standard signal).
Tips & Warnings
ATSC cards can only receive over-the-air signals (i.e. from an antenna) unless your TV tuner card has a cablecard slot. If you do have a cable card slot, you can request a cable card from your cable company to replace your cable box and simply slide it into the slot on your TV card.
Be sure to ground yourself by touching a metal part of your computer case before you work inside your computer. Otherwise, you could damage the delicate components of your computer with static electricity.
References
Mygica A680B ATSC TV Stick
Microsoft: How to Install and Configure a TV Tuner
Build Easy PC: Install TV Card