NVIDIA has released its GeForce 181.22 Beta driver for Windows XP and Windows Vista, you can get it over here. The changelog suggests this driver has some tweaks for Mirror's Edge.
This driver is recommended for the optimal GPU PhysX experience in EA’s hot PC title Mirror’s Edge.
GPU PhysX is supported on all GeForce 8-series, 9-series and 200-series GPUs with a minimum of 256MB dedicated graphics memory. This driver package automatically installs PhysX System Software version 9.09.0010.