Now that we’re all using XCode 3.2 on Snow Leopard (you are, right?) and building 64-bit apps you may find that not everything 64-bit works when your app is run on Leopard. Loren Brichter of Tweetie fame found that Tweeite launched much more slowly on Leopard and I found that 32-bit web plugins (read Flash) do not load in a WebView in a 64-bit app in Leopard.
There’s an Apple approved and supported method for limiting architectures to Mac OS X versions. Here’s how to limit 32/64-bit Intel apps to only run 64-bit Intel on 10.6.0 and later.
Open your application’s Info.plist in a text editor and add the following before the final
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<key>LSMinimumSystemVersionByArchitecture</key> <dict> <key>x86_64</key> <string>10.6.0</string> </dict>