A maximum of 2 displays is supported with Windows XP. Activating a 3rd or 4th display in Windows XP will not work due to Operating System and software limitations, but is supported in newer version sof Windows.
GeForce 600 series cards do not support 3+ displays on Windows XP.
Updated 05/16/2013 09:42 AM
Why can I not activate all 3 monitors on my GeForce 600 series graphics card using Windows XP?