Here are some small working iOS example projects compatible with XCode 4.5+ with a recent build of the openCV framework:
See if you can get one of those running (they should not require any modifications), then try drag the openCV framework into your project.
You may have issues if you are running xcode4.3, as most of these were created using Xcode 4.5. But this one:
http://www.github.com/foundry/OpenCVSquaresSL
Has three targets. The SL target uses an openCV framework and build settings designed to run with XCode 4.2 under Snow Leopard, it will probably work if the others don't.
Alternatively - better - upgrade to current XCode (4.6)