I have some UIViewControllers from my old iOS4 project, they are using .xib, created in interface builder.
My new project, built for iOS5, uses storyboards.
You could copy the contents of the xib into the storyboard and then instantiate it using:
- (id)instantiateViewControllerWithIdentifier:(NSString *)identifier
after setting the identifier on it. If you need the instance of the storyboard you can get it this way:
[UIStoryboard storyboardWithName:@"MainStoryboard" bundle:nil];
You cannot mix xibs and storyboards in your project -- it's one of the other, I'm afraid.
Mike K's answer is false.
While mixing XIBs and Storyboards doesn't really solve Alex's problem, it is quite possible to do within the same project.
See: https://stackoverflow.com/a/8516479/1309238 re: loading a second storyboard.
I'm not sure if including a "Main Storyboard" in your Target Summary is advisable if you plan to do this, but if you've loaded a XIB instead of a storyboard to begin with, you can modify the code linked above to load the storyboard after the XIB.
I'm not sure if you can jump into the middle of a storyboard from a XIB, which may have been what Mike meant.