I know this article is a hundred years old, but in case anyone is wondering how to address this issue in more recent Xcode versions (as opposed to Xcode 3), you'll find the appropriate setting labeled Always Show Disassembly under Debug>Debug Workflow in Xcode 6 and up. Ensure the option is NOT checked.
In Xcode 5, the option was labeled Show Disassembly When Debugging under Debug>Debug Workflow. Ensure that "Show Disassembly When Debugging" is unchecked.
Back in Xcode 4, the Show Disassembly When Debugging setting was found under Product>Debug Workflow. Again, ensure that the option remains unchecked.
This was driving me crazy, too.
NOTE: The information above is still valid for Xcode 13+. I've applied updates to this answer as new versions of Xcode have been released. Fortunately, the option has remained unchanged since Xcode 6 (so far).
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