NVIDIA®'s NVRotate™ --bundled with ForceWare software for desktop, workstation, platform, and mobile solutions--allows users to pivot any display connected to an NVIDIA GPU from landscape to portrait mode, for easier information and application viewing. Many LCD flat panels support rotate (or pivot) mode natively within their monitor stand, but lack the software to provide full hardware acceleration for 2D and 3D applications, and video playback.

The XP driver you are using either does not provide the hardware acceleration when using NVRotate, or you have it turned off. Your CPU is doing the rendering. What are the specs for your computer(s)?