By far the easiest way to get Oracle up and running on OS X is to install VirtualBox and run a developer VM. The VirtualBox and VMs are free downloads from Oracle. You don't have to install the database and the developer VM comes with labs to get you started.
So what could make it even better? Well, the VM needs memory and CPU, and my laptop is old and feeble (the problem with "laptop RAC" alas). What if I could install the VM on a desktop and just ssh into it from my older, low-powered low-memory laptop?