I would recommend not using LVM within a VM because it makes it harder to back up the files within the VM
/usr/sbin/lvcreate -L 5G -n vm_testvm VolGroup00 #first create a logical volume for the machine
/usr/sbin/lvcreate -L 512M -n vm_testvm_swp VolGroup00 #create the LV swap file
/sbin/mkswap /dev/VolGroup00/vm_testvm_swp