Some of us play with operating systems just for the heck of it. Some set up their systems to do a multiple-boot scheme where two or more OSes are installed on different partitions of the machine. However there are some who don’t have the time to clear up their existing systems for this scheme, so the alternative would be to use virtualization, where another OS runs on top of what is currently running.
We have Parallels and VMWare to do virtualization. However these are commercial products, so some amount of money is required to be able to use it legally. Just recently, Sun releases its own virtualization product, FREE and OPEN SOURCE!
You can know more about this product at the VirtualBox home page.
Coincidentally there is a video presentation (~16Mb) at MacWorld that discusses what it is, how you can use it, and how it performs.
I’d try using this with an image of Ubuntu Hardy Heron. I’ll be posting the results later.