Many restaurants will not be accepting reservations this early. Most NYC restaurants take reservations 31, 30, or 28 days in advance. The only one I can think of offhand that does them two months in advance is Le Bernardin but their policy is that they open up the books on the 1st of every month for the month following. For example, you'd need to call on October 1st for Thanksgiving Day (assuming they are going to be open).
Here's some lists of places who served Thanksgiving in 2010:
As you can see, there are actually a lot of places open in NYC so you do have a good number of options. Lots of restaurants, though, probably won't know their plans for another few weeks -- I'd start researching restaurants that look good to you now but only start calling around in mid-October to ask about what they're planning.
155 W. 51st St., New York, NY 10019
Good Call. I was thinking the same thing for myself. My issue is that holidays always seem to be a bust at restaurants, even the good/ $$$$ ones. Since it's only my mother and I we go out but I have yet to find a place within NYC that really does this holiday justice. I have good recs for Westchester if you are interested. But hopefully we get some good nyc tips here! :)