This guide details how to prepare Centos 5.3 for an Oracle install. I'm running CentOS inside a VM using KVM. Since I'm setting up a test Oracle install because I'm studying for an OCA, my database needs are pretty simple. An Oracle install requires a non-trivial amount of OS prep work, so I'm writing about the experience here.
VirtualBox has been great for me, but I thought I'd give KVM/qemu a try. I'd tried running Bochs around 2003 and it was exciting to see that it actually worked, but the poor performance made it more of a novelty than a useful tool. It's nice to see how far Qemu it's come in this time. It's not only usable but quite handy, with simple CLI management and excellent performance.