I knew absolutely nothing about Linux when i first found the DSL community and I want to encourage you to keep reading and learning. The community here is very supportive and I quickly became far more comfortable with DSL than I was with the "normal" newbie distros of the day, such as Mandrake, Mepis, Kubuntu, etc. simply because I felt respected and was not afraid to ask questions and talk about my oopsies.
That said, I am currently running DSL on Virtual Machine within my Ubuntu box. I would love to get rid of Ubuntu for philosophical reasons: I want to move away from proprietary software altogether and even though my older son bought me a System76 Wildebeest for Christmas '11, not everybody is lucky enough to be able to afford that kind of hardware and I'd really rather spend my time here than feeling sorry for myself that the Beest isn't going to be new and shiny and fast forever. I have to accept the fact that ditching Ubuntu isn't going to happen right away, though, because I have a five year old younger son and other things going on in my life. At least I'm not stuck on the consumer treadmill trying to save up money for a Windows 8 machine, anyway, so i consider myself fortunate.
If you don't have a dedicated DSL machine, you can still learn quite a bit from running off the CD or a virtual machine. You didn't mention the specs of your Ubuntu box, but if you have enough RAM, Oracle Virtualbox is right in the reps and it's ridiculously easy to install and use. I'm kicking myself for thinking I wasn't smart enough to understand it for so long.
RAM is cheap and DSL isn't very resource intensive, so you might find yourself using your guest (virtual machine) more than your host (Ubuntu install) over the course of time as things start making more and more sense to you.
Enjoy the journey rather than racing to the destination. You're in the right place to begin an adventure that could change your entire way of looking at computers and human nature.
As the person who first told me about DSL would say, "Welcome to the revolution".
Blecch, I wanted my first post to be a re-introduction but I guess I'm still me if anyone even remembers me any more.