Paul Scarlett of tressleworks.ca has created a Visual Basic Script to re-package DNN 4.0 skins into the new format for DNN 5.0.
The script is designed to unzip an existing skin/container package and then generate the appropriate manifest and then repackage it back up for deployment to a DNN 5.0 site.
He makes mention of requiring the following library to be installed on your system: XStandard XZip library.
Download DotNetNuke Skin Repackaging Script