Do you need the latest version of Xcode to submit apps to the app stores? I am currently using Xcode 3.1.3 on a mid 2009 MacBook Pro running Leopard. Don't want to upgrade if I don't have to.
I don't think so... although unless I'm mistaken Xcode 3 didn't have the ability to upload the binary directly to Apple and instead relied on a separate Application Uploader (I can't remember the exact name,) to do it.
So you'll either need to find a copy of that uploader, or upgrade to Xcode 4.
Edit: The name of the application you need to get your app on the app store using Xcode 3 is Application Loader. Application Loader, however, requires a minimum OS version of 10.6.8.