The Microsoft Bluetooth stack is included in Service Pack 2 for Windows XP. The Microsoft Bluetooth stack for Windows XP Service Pack 1 is also available. Please refer to Microsoft Knowledge Base Article 323183: Availability of Windows XP Service Pack 1 Support for Bluetooth Wireless Devices. The update package (Q323183_WXP_SP2_x86_Enu.exe) that is discussed in this article is available to download at: http://download.microsoft.com/download/whistler/SP/1.1.1/WXP/EN-US/bt_stack_rtm.exe