I'm finding this v frustrating too. Have reflashed to no avail (using the Nokia install wizard - I might try manually next). I managed to install devicescape but not Canola, Streamtuner or Vagalume.

The problem for me seems to be the Preinstalled Nokia catalogues - certified, non certified and Nokia System Update.

Looking at http://gronmayer.com/it/index.php?lang=en&system=maemo4 it indicates that non certified and update are online but empty. Otherwise I might've tried deleting the ones on my N800 and reinstalling them. Although I'm not sure if the Nokia system update can be deleted.

I only bought my N800 last week and I'm tearing my hair out!

Rather than tear your hair out, don't focus on doing the impossible. It sounds like there is a temporary problem. There are other media programs out there.
Lots of them.