Desktop folder has become a "package"

Hello:

I have three concurrent problems on a MacBook Pro < 3 months old, which I think I can trace to an "Arrange by" command in the Finder when I had an external (back-up) hard drive connected. I was running Aperture at the time.

First: I cannot access the Desktop folder from the Finder sidebar. I get this message: There is no default application specified to open the document “Desktop”. There is no arrow beside the Desktop folder in the sidebar to allow it to toggle open. Apparently, the Desktop folder has become a "package." If I show the package contents, everything that should be there is there. How do I turn this package back into a normal Desktop folder? I have searched the discussion forums and have run the various Terminal scripts suggested, and have trashed Finder and sidebar .plists and relaunched the Finder, to no avail.

Second: This is probably related to the first problem. When I click on the Desktop, the New Folder command in the Finder is dimmed. I can create a new folder when I access the Finder through the sidebar, but then I cannot drag that folder to the Desktop itself. I get the "no smoking" symbol when I drag over the Desktop. I can, however, drag such a folder to the Trash.

Third: This one really baffles me. My HD on the MacBook Pro has become an amalgamation of that computer and a back-up of my iBook G4 that was on the external hard drive. The MacBook Pro HD includes System 9 stuff that won't even run on the newer computer. I know that I did not physically drag the older computer's back-up onto the newer one's HD icon. I have no idea how this happened – maybe it was during that "Arrange by" command? - but perhaps it is contributing to the other two points, noted above.

I would appreciate any suggested solutions. At the moment I am saving all my work to an external drive in case more folders become inaccessible. Thanks!