The installation/upgrade process for Fedora 12 is similar to Fedora 11: http://blog.iwayvietnam.com/tuanta/2009/08/13/fedora-11-installation-process/.
Fedora 12 local repositories in iWay LAN has been also ready. See /etc/yum.repos.d/local.repo below:
# Base packages inside iWay LAN
[base-local]
name=Fedora $releasever – $basearch – Base local
baseurl=http://dev.iwayvietnam.com/mirror/f12/
enabled=1
gpgcheck=0
# Update packages inside iWay LAN
[updates-local]
name=Fedora $releasever – $basearch – Updates local
baseurl=http://mirror.iwayvietnam.com:9090/yum/updates/$releasever/$basearch/
enabled=1
gpgcheck=0
# Additional packages at ATRPMS.net
[atrpms]
name=Fedora Core $releasever – $basearch – ATrpms
baseurl=http://dl.atrpms.net/f$releasever-$basearch/atrpms/stable
gpgkey=http://ATrpms.net/RPM-GPG-KEY.atrpms
gpgcheck=1
enabled=1
Have fun!