VirtualBox

Create a VM
VBoxManage –help


VBoxManage createvm --name "MyvmServer" --register
VBoxManage modifyvm "MyvmServer" --memory 256 --acpi on --boot1 dvd --nic1 bridged --bridgeadapter1 eth0
VBoxManage createhd --filename MyvmServer.vdi --size 10000 --register
VBoxManage storagectl "MyvmServer" --name "IDE Controller" --add ide
VBoxManage storageattach "MyvmServer" --storagectl "IDE Controller" --port 0 --device 0 --type hdd --medium MyvmServer.vdi
VBoxManage storageattach "MyvmServer" --storagectl "IDE Controller" --port 1 --device 0 --type dvddrive --medium /home/MyvmServer.iso


Start a VM with VboxHeadless
VBoxHeadless --startvm "MyvmServer"
VBoxManage controlvm "MyvmServer" poweroff
VBoxManage controlvm "MyvmServer" pause
VBoxManage controlvm "MyvmServer" reset
VBoxHeadless –help

Import an existing VM
VM with the name myvm that needs to be reused. A directory contains myvm in the VirtualBox directory. The myvm directory will contain the myvm.xml file. Copy the myvm directory (including the myvm.xml file) to the new Machines directory.
In addition copy the myvm.vdi file from the old VDI directory to the new one.
Register the imported VM:
VBoxManage registervm somedirectory/myvm/myvm.xml

Reference Page
The above link contains more info on VM's.

Remove CentOS Xen

Install Standard Kernel
yum install kernel

Remove Xen Kernel
yum remove xen kernel-xen

Edit Grub to Select Correct Kernel
/boot/grub/grub.conf