I am trying to build an app bundle with py2app on Mac OS X 10.6. The app uses some libraries which are only compiled for 32-bit, so when the app is run there is an ImportErr
If you want to run only in 32 bit mode, then you don't need the 64 bit architecture. So you can just strip out all the non-i386 architectures from your resulting application bundle using the ditto
utility.
Example:
ditto --rsrc --arch i386 YourApplication.app YourApplicationStripped.app
Your application bundle will be smaller and will run as a 32 bit application for sure, even on 64 bit Intel systems.
Manual: http://developer.apple.com/library/mac/#documentation/Darwin/Reference/ManPages/man1/ditto.1.html
Or just run in a terminal: man ditto