Microsoft is giving free upgrade for your Windows XP to Vista if you purchase any PC between 26-Oct 2006 and 15-Mar 2007.
Are you happy with Windows XP? Or you prefer Windows 2000 or even older like Windows 98, Windows 3.1 or MSDOS 6.22 O_o.
When 80286-age, we use 10% of the CPU power for UI, 90% for application and now we use 90% got the GUI and 10% for the application. In order to let you feel the same speed or faster speed, we need to boost up the CPU power so you wouldn't feel the burden of running applications.
I admire Linux, although I still using Windows for daily application. An old PC (PII type) can perform like Windows XP using Linux.
We can't deny that installing Linux and bring up the X is a challenging task, but sooner this will not be a problem when more and more support form hardware manufacturers and more and more programmers / communities help to engineer the Linux core.
Linux are customizable, while for Windows, you can't even can choose to install or not to install IE. But customizable also lead a problem - too much of distribution choices. I'm not sure about you, but choosing a suitable distribution is just as difficult as choosing a wife from bunch of girl friends :).