Sent by HarrisEditor: Harris, this is a great question. Full disclosure: I cooked Thanksgiving for six a couple years ago, and didn't buy anything new — for the kitchen, that is. I did buy a couple of extra white bowls and platters; I needed them anyway, and I knew that my servingware was going to be stretched to the max with all the extras of Thanksgiving!
Before giving advice on the specifics, I would suggest sitting down with the list of the dishes you are making. Walk through each step of each recipe mentally, asking yourself if you have things your kitchen to handle each step. Finish by making sure that you have serving dishes for each recipe.
Then see where you're squeezed or don't have enough equipment and start there.
Many people feel that they need a roasting pan, but unless you're roasting a huge turkey, I find that a metal 9x13 (or a large sauté pan) pan does just fine for most roasting jobs. And you can construct a rack out of aluminum foil, too.
Readers, any suggestions for Harris and his Thanksgiving kitchen?