This example explains how to work with backlight without any drivers. It was written for Asus p525 device, but should work on any device with Intel pxa27x CPU. To compile project you need VS2008 and WM6.0 SDK.

华硕x101CH上网本显卡网卡驱动for WINXP-The ASUS x101CH netbook graphics card driver for WINXP