[self.navigationController setToolbarHidden:YES];
Here's more of an example:
- (void)applicationDidFinishLaunching:(UIApplication *)application 
{
    self.window = [[[UIWindow alloc] initWithFrame:CGRectMake(0,0,320,480)] autorelease];
    RootViewController *rootViewController = [[[RootViewController alloc] initWithStyle:UITableViewStyleGrouped] autorelease];
    self.navigationController = [[[UINavigationController alloc] initWithRootViewController:rootViewController] autorelease];
    navigationController.toolbarHidden = YES;
    [window addSubview:[navigationController view]];
    [window makeKeyAndVisible];
}
                  Jordan
                   2009-11-03 00:29:50