Bashiok reports World of Warcraft: Mists of Pandaria won’t be playable on Windows 2000 systems, and encourages users to upgrade their Operating System prior to the transition.

As you might remember, there will be patch or series of patches prior to the next expansion updating the core World of Warcraft folder, like when Cataclysm content was available for those who didn’t have the expansion.

Bashiok: In preparation for the upcoming release of Mists of Pandaria, updates to World of Warcraft will no longer support Microsoft Windows 2000. Microsoft ceased support for this version of their operating system in 2010. Players still using Windows 2000 are encouraged to upgrade prior to the release of Mists of Pandaria. — Source

It’s recommended to upgrade to Windows 7. Make sure to upgrade to the correct version: 32-bit or 64-bit.

Those who wish to upgrade their computer here are some recommendations:

When it comes to Laptops you should consider Intel Core i7 CPU, and make sure it contains a good graphic card such as the Nvidia GTX 560M 2GB GDDR5, the AMD Radeon HD 6870M (or better).