Resources and the Resource Manager still exist in Carbon, but have been mostly replaced with Nibs. You can use custom Document Bundles instead of resources to help you organize your documents items.
If you do use Resources you will want to move them out of the resource fork and into a data fork of their own file. The resource data fork can then be placed in the application's, or document's bundle.
I found this application [Resorcerer] helpful in getting resources out of old programs. It will also let you save resources in the data fork.
In Xcode 2.1, you must use data fork resource file in your Xcode project. Furthermore, the file extension has to be ".rsrc". In Xcode 2.3, you can also use resource fork resource files, and you can use the extension ".ppob".
When dragging the data fork resource file onto the Xcode project window, you need to specify how to handle the data fork resource file.
By default, Xcode will place the resource file under "Copy Bundle Resources" build phase, which will just copy the exact file into the /Resources folder inside the application bundle. If you need to utilize the resources by using Carbon's Resource Manager API's, you would need to specify a separate build phase called "Build ResourceManager Resources".
Once the data fork resource file is specified, you can further specify to merge the resource data into AppName.rsrc (global resources container) or inside one of the .lproj folders.
Comparing Resources has links on notes on ways to compare and merge resource files.