wget http://packages.sw.be/rpmforge-release/rpmforge-release-0.5.2-2.el6.rf.i686.rpm
rpm -ivh rpmforge-release-0.5.2-2.el6.rf.i686.rpm
cd /etc/yum.repos.d
wget http://download.virtualbox.org/virtualbox/rpm/rhel/virtualbox.repo
yum --enablerepo rpmforge install dkms
yum groupinstall "Development Tools"
yum install kernel-devel
yum install VirtualBox-4.2