The Moment Of Truth
You're almost there. Now crack open the user manual and look for anything in the index about PC support.
Why? Because, it will make your life easier. There is no actual standard about how an HDTV should support with a PC, or about how an HDTV should handle resolutions that are not the same as its native resolution. Feeding an HDTV a 640x480 resolution over HDMI, for example, could have unexpected results. What results might those be? Hard to say. Rumor has it that some HDTVs can be broken by doing this, but it must clarified that this is a rumor. I've never seen it happen and never seen anyone provide evidence that it happened. But since there is nothing saying that an HDTV should work with that sort of resolution, it is best to be cautious. Keep an eye out for any warnings and instructions that your user manual gives you. If you don't see any warnings - and you probably won't - then great. Go ahead and plug it in. If you do, then do what the manual says. At the least, you probably won't get a picture until you follow the manual's instructions.
Having read the manual, the moment of truth arrives. Plug in all connections and fire up the computer. Chances are good you'll have to do that before attempting to change the HDTV to the proper input, as many HDTVs will not allow you to scroll through inputs that are not receiving a signal. And that's probably it. If your computer auto-detected the HDTV and changed all settings as needed, like it is supposed to, then you should not even have to change the resolution. If your computer did not auto-detect correctly, no problem. Simply set the resolution to what it should be, as you would with any other monitor.
And that's it. In the end, actually getting the HDTV to work correctly is much easier than finding the right HDTV and making sure your PC will support it properly. Now go to Hulu, ABC, or any number of network websites and enjoy some free, high-def content!