Under System 7 and above, these settings are stored in the Finder Preferences file. It is located in the Preferences folder inside the System Folder.
If this file has become damaged or corrupted, you should move it to the Trash so that another one can be created. Once the file has been moved to the Trash, restart your Macintosh computer. A new Finder Preferences file will automatically be created. Empty the Trash after you restart. This should allow your system to remember the settings.
For a complete list of what is stored in the Finder Preferences file, see Technical Information Library (TIL) article # 17981, named "System 7.5 : Default System Preferences".