If you're taking the NIB-approach, then presumably in your MainWindow.nib, you have a UINavigationController (or a UITabBarController) with a root view controller (or a controller for each tab).
First of all, create a new view NIB for your UITableViewController sub-class. Then, select the root view controller in your MainWindow.nib and in the inspector, under "NIB Name", enter the name of your custom NIB.
It should look something like this:
This root view controller is your custom UITableViewController sub-class.
Now open the view NIB you just created. Delete the empty view and drag in a UITableView. Select the File's Owner object and set its class to your UITableViewController sub-class in the inspector panel:
You can now select the table view and play about with its properties in the inspector panel.
Finally, don't forget to hook up the table view outlets; it should be set as the view for the File's Owner, and the File's Owner should be set as the delegate and dataSource for the table view.