I think you are the first person in history to know what DLNA means but NOT to know what an HTPC is.
HTPC = Home Theater PC, or a computer that you use (mostly) dedicated to streaming video, music, etc. to a home theater system.
What JD was suggesting was that, if your computer is close enough to the AV setup, that you could make a direct video connection instead of trying to put the video files on a USB stick. If your PC isn't anywhere near your AV system then it probably won't work and you will need some intermediary solution.
In terms of your question, whether it's Airplay, DLNA, USB interface, etc. the receiver is simply not set up to stream computer video files. It's basically an audio streaming solution only. You should check though as many other devices like Blu-ray players, PS3, etc. have a USB port that can stream video, so you might already own something that will work even if the receiver can't do it directly.
My TV has a USB as well...would that work? I guess the problem with that is it wouldn't circulate the audio through the AVR, even if it did work?
Yes, that *should* work. You can pipe audio back to the AVR either by using the digital audio output on the back of your TV, or (if your TV is fairly recent) by using the ARC (audio return channel) feature to pipe audio back down the HDMI monitor connection.