The first thing to do after you have a working PC is install an operating system
(OS). You can select from several available on the internet or from your local
computer store. The first option, and the one taken by most people, is to install
Microsoft Windows, of which the current version is Windows Vista. Another
option is to install a GNU/Linux distribution (a Free Software operating system).
There are many other operating systems to choose from as well, notably
the very famous Linux but let us not forget other free operating systems, such as
BSDs. Note that you also have the option of installing more than one operating
system in what is called a multiboot setup.
If you are going to install both, install Windows XP first. This is because
Windows overwrites the software that GNU/Linux requires to start up, even
if something’s already there. If you install Windows before all of your other
systems, you will be able to easily boot into all of them.
Choosing between Microsoft Windows, GNU/Linux, or one of the other operating
systems is largely depependent on what software you need to run. Simply
put, can you accomplish your day to day tasks with the software that will run
under the operating system in question? Microsoft Windows is better in terms
of software availability, hardware compatability and support, but GNU/Linux
wins in terms of stability, ability to run on older equipment, and cost. Both
systems have a range of software, but determine your needs before installing
either operating system.
Note that, having installed Windows, you can always install GNU/Linux
later and, conversely, if you install GNU/Linux first, there is no throwaway cost
to regret if it turns out later that you need Windows.