macOS Opening .NIB file problem

Hi,

I downloaded an example here:
http://developer.apple.com/samplecode/Reducer/index.html#//apple_ref/doc/uid/DTS10003626

And I can't open .nib file. How to solve this problem?

Thanks.

P.S. I open it under Leopard 10.5.6., Xcode 3.1

I've compiled CollapsibleBox. But I still can't open .nib file
Could you please send me compiled src code at sotrosh@gmail.com ?

Thanks in advance.