In our previous house I had a Tivo with the Tivo wireless adapter connecting to an Airport Extreme. Streaming video worked just fine. Not quite as fast as hard-wired. The only real issue I had was that periodically the Tivo would give a network error, that many times could only be resolved by a restart. After researching it, I found it was a fairly common problem using the Tivo wireless device. Not sure if you would have that problem if you were stringing the Tivo off an Airport Express. In our current house the Internet comes into the room with the TV, so I'm now hard-wired.
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Captain Kirk: "Once again we've saved civilization as we know it."
Dr. McCoy: "And the good news is they're not going to prosecute."