Welcome - Ubuntu: Linux for human beings
We all heard about UNIX and how secure and stable it is, comparing to Windows.
UNIX is an open source Operating System. That is, the code it is made of, is available to the public and anyone can add to it, and it is mostly free.
What kept UNIX from gaining market and popularity is that is was difficult to operate, but not anymore. Ubuntu is one OS based on UNIX that gives the Windows-like environment while preserving the stability and security of UNIX.
After downloading Ubuntu and burning it to a CD, you restart your computer and run Ubuntu on your computer from the CD where you have an option to install it. You don't need to install it, but you will not have Ubuntu's full capabilities.
I installed Ubuntu on my Compaq Presario V2000 laptop without problems. Everything worked fine except for the Wireless Network Card :o(
If you have an old system, don't throw it. Install a new copy of Ubuntu on it and it will become new again.