I assume you're referring to Ubuntu. And yes, as it is a linux OS, of course you can practice using it.
Ubuntu was my first Linux OS... You can get it using a Live CD or install the full OS through VirtualBox
What are you trying to achive by practising linux commands? There is no better way to practice than using a Linux system as your primary OS for a while. There are plenty ways to try this out. How To's are all over the internet. You could setup a VM or use Wubi to install Ubuntu on Windows essentially as an application, or go the whole hog and actually install it onto your tin.
The best way to learn Linux commands is to actually use Linux. Start with a distro like Ubuntu. From my experience their community has the best support and you don't have to install it. You can run it directly off the CD. Or you can get Knoppix, burn it to a CD-RW and run it as your Linux OS. With that one, you can actually save files and make changes directly to the OS without having to actually install it.
Windows XP/2000 command list that will make any Linux user feel at home at the command prompt. A lot of these commands are intended for administrating a network, but they are great for savvy home users as well. We even listed which OS you need for these commands.
I am not sure if it is considered polite in this community to hijack other peoples thread ;) but I will answer you anyway.
A good starter to the world of Linux is, in my humble opinion, to install Linux Mint on an old computer or dualboot it if you only have one. Why Mint? Because Mint is based on Debian and Ubuntu and is very easy to learn to use for a Windows user.
I also think you should read nonshatters post (post #2 in this thread).
To learn simple Linux command you can just Google.