If I were you, I'd go to
http://ubuntu.com/ and download and burn that ISO. It is the most used distro right now by most estimates (although Fedora and OpenSuse are close and at times have beaten it recently). It is a normal distro that you install, but the install CD boots into a LiveCD and you can run it without installing.
If you don't like the look and feel of it, then try Kubuntu (http://kubuntu.com ) instead. It is the same base system with an entirely different desktop enviroment, KDE. KDE is a bit more Windows- (and, in terms of eye-candy, OS X-) like and perfect if you like eye candy (although you can't really use all that eye candy off of the CD; to get the full KDE experience, you need to install it).