Microsoft had made a surprised decision to stop producing Windows XP, we know that Windows XP itself is quite a famous operating system.
Microsoft already stopped to distribute Windows XP to several famous computer vendors which bundled Windows XP to their computer. According to some opinions, this decision
is made as an effort of Microsoft to maximize their customers' transition to their new product, Windows Vista and Windows 7 which according to plan, it will be released on 2010.

But for an exception, Microsoft will still provide Windows XP for ultra-low-cost PCs and laptops project such as made by Asus through its Eee PC. This support will end till 2010, and the
main purpose is to prevent Linux monopoly these 'cheap' notebook and PC.

More information, follow below sources...

BeritaNet
BBC News
Informationweek