Sorry for the newbie question. I have a UITabBar in my main window view as well as an array of UINavigationControllers for each Tab. The structure is similar to the iPod a
[myTabBarController setSelectedIndex:index]
EDIT: Answering the part 2 question from the comment:
You can define a method in AppDelegate for switching to a different tab.
And you can get hold of appdelegate from anywhere and send a message.. something like:
MyAppDelegate *appDelegate = (MyAppDelegate*) [[UIApplication sharedApplication] delegate];
[appDelegate SwitchToTab:index]