You're getting errors because the linker can't find the OpenGL framework. This is an unusual problem because the OpenGL framework is one of Apple's frameworks, and Apple's frameworks normally work well with Xcode right out of the box.

The first thing you should do is turn off ZeroLink and try to build the debug version of your program. If you're running a recent version of Xcode, choose Build > Allow ZeroLink to turn it off.

If turning off ZeroLink doesn't solve the problem, make sure you're linking the OpenGL framework. In the Groups and Files list, there should be a disclosure triangle next to Targets. Click it to see your project's target. Click the target's disclosure triangle to see its build phases. Select the Link Binary with Libraries build phase and make sure the OpenGL framework is in that build phase. If it's not, drag the OpenGL framework from the Frameworks folder (click the disclosure triangle next to the project name in the Groups and Files list) to the Link Binary with Libraries build phase.

If you are linking the OpenGL framework, you may need to add a search path to the OpenGL framework. Select the name of your project from the Groups and Files list and click the Info button in the project window toolbar. This will open the project's information panel. Click the Build tab in the information panel. Choose Search Paths from the Collection popup menu. Add a path to the OpenGL framework to the Framework Search Paths build setting.

If that doesn't work, I don't know what to tell you. You may need to reinstall Xcode. Normally Xcode automatically knows about the OpenGL framework. All you have to do is add it to the project. And the SDL OpenGL template project should compile with no problems.

The OpenGL framework comes with Mac OS X. I've never seen the framework available as a separate download so you would have to reinstall Mac OS X if reinstalling Xcode doesn't solve your problem.