After you create a SplitView project, open up the RootViewController.m file and look at the -tableViewDidSelectRowAtIndexPath method. You'll see that the item that you clicked is then set as a property of the DetailViewController.
The design you're looking for would require that you push another view controller onto the navigation stack. So if you imagine the e-mail application, when a user picks a folder, the detailView is not updated, but the next level of the Inbox is pushed onto the stack. When a user selects a message from the inbox, the detail view is updated with the message contents, and the RootViewController just stays where it's at.
in the -tableViewDidSelectRowAtIndexPath method, declare your new view controller
NextViewController *nextView = [[NextViewController alloc] initWithStyle:UITableViewStylePlain];
//This assumes you have another table view controller called NextViewController
//We assign it to the instance variable "nextView"
[self.navigationController pushViewController:nextView animated:YES];
//tells the navigation controller to "slide" the "nextView" instance on top
//if animated:NO it wouldn't slide, it would just "update"
[nextView release];
//release the viewController, it's now retained automatically by the NavigationController
Does this make sense?