You don't say what operating system you're using. Since permissions are handled in very OS-specific ways, this makes it hard to help.

If you're using Windows NT, the regular Unix file permission bits aren't terribly useful. NT has a more elaborate and fine-grained permission system than the standard Unix one. For NT, you should look at Win32::FileSecurity in libwin32. Likewise, there are different modules for Solaris, DCE, and other ACL schemes.