Thanks for your answer! All linux-kernel-based OS on GPL are open source - which is not the same as "free" in this context. But nearly all of them are free also. There are a lot of very nice and useful alternatives to Ubuntu out there, but I better do not start some Linux-Flame-War here ... I am an absolute computer idiot, but I have been using Linux distributions for 10 years now without any problems. I couldn't live without it! But if you are happy with Windows - why not? Never change a running system - wasn't it like that?