Along with Virtualmin support for CentOS 6, we have now made available pre-built images for KVM and Xen containing CentOS 6. For each virtualization type we have images with the base OS, Virtualmin GPL and Virtualmin Pro.
The KVM images have full support for VirtIO networking and disk images, which provide a significant speedup over pure hardware emulation. The Xen images support para-virtualization, and use a single-partition format for maximum flexibility.
The latest images can be downloaded from within Cloudmin at Cloudmin Settings -> New System Images, by checking the box next to the images you want to use, and clicking the Download Selected button.