Hi have upgrade system from fc1 to fc2 without no problem
after to upgrade to fc3 i have do

rpm --import /usr/share/rhn/RPM-GPG-KEY-fedora


There a bug with that,
the doc sais verify that the Fedora Project gpg key is installed with this
rpm -q gpg-pubkey-6b8d79e6-3f49313d

the output:
package gpg-pubkey-6b8d79e6-3f49313d is not installed

If this key is not installed, and you are running Fedora Core, you may install it with:
rpm --import /usr/share/rhn/RPM-GPG-KEY-fedora

every thing looks good...

rpm -Uvh fedora-release-3-8.i386.rpm yum-2.1.11-3.noarch.rpm
rpm -Uvh --force fedora-release-3-8.i386.rpm yum-2.1.11-3.noarch.rpm
yum upgrade

And this is the out put of the yum command:
Traceback (most recent call last):
  File "/usr/bin/yum", line 6, in ?
    import yummain
  File "/usr/share/yum-cli/yummain.py", line 23, in ?
    import yum
ImportError: No module named yum

What's the probleme !?!