Since upgrading to xcode 4, I can't find where to specify what Target a resource belongs to. Previously, I selected the file and hit command+i, but this now seems to run the program, rather than bring up the info box for that file.
Select the project file in the document explorer. On the Right margin of the Xcode window make sure to display the right drawer view if it isn't already there (it usually has Object library and Quick Help). In the top margin, click on the icon that looks like a document (rather than the one with the waves that is quick help). The target membership and the other info from the old Get Info command is there.