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Before buying one of these gadgets, there are a few things to check. For instance, AppleTV and GoogleTV will connect only to TVs that have the secure connection system known as HDMI.
You'll also need a home network that's fast enough to handle video. Most of the new wireless adapters take advantage of the faster speeds of equipment meeting the 802.11n Wi-Fi standard, but may work with the slower but more common flavor, 802.11g.
If you don't want to install or upgrade a Wi-Fi network at home, you can extend a wired connection to the TV with the proper cables. Or you can get "powerline" devices that extend network access through home electrical wiring to the TV set, where they connect with an Ethernet cable. Kits cost under $100.