You can check the version of your Windows Media Player from the Help menu. Open WMP and press Alt > Help > About. The version will be displayed in numbers divided in 4 groups. Latest version available is: 12.0.7601.17514. The version has some meanings:
- 12.0 = The version of Windows Media Player
- 7601 = The build number of your operating system
- 17514 = The build number assigned by the latest hotfix installed for Windows Media Player.