Three million web forum postings contain wrong, misguided or overly complex solutions, so here:
When ubuntu complains
WARNING: untrusted versions of the
following packages will be installed, that's because of bad data
in the keyring for ubuntu packages, which is part of the package
ubuntu-keyring. This is a
known bug and there is a workaround: to reinstall windows.
sudo apt-get install --reinstall ubuntu-keyring