If you have a system with around 12 GB of free disk space and 1+ GB of memory as well as a reasonable CPU (2 Ghz), why not try the Oracle 10g Release 2 Desktop Data Center. I installed it on my Centrino Notebook which has 1.5 GB memory.
It includes a VM (virtual Machine) and ReadHat Linux as well as a RAC Installation of Oracle 10g R2. It takes around an hour to install (you only have to switch DVD's once). Then you have full access to a trial version of a pre-configured 10g instance. I found it particularly interesting to take a look at some of the Warehouse Builder functionality. Also being able to access the example data and front-end for OLAP was useful.
If you have time take a look at it. When you're finished, simply drop the VM, and it's all gone!
You can order a copy at this address here or by free phone 1.800.633.0821.
