Add the FC4 repository to your yum configuration (enable=0). When you want to install an FC4 package (for example):
yum --enablerepo=fc4 install packagename
Yum will then be able to pull in the dependencies from the FC4 repository as needed. Be careful, sometimes the dependency list for an operation like this can be huge. Never use the '-y' option in this case, or you will end up (mostly) upgrading to the FC4 test release.
