NVIDIA has published a new version of PhysX System Software. This new version 9.09.0408 is WHQL certified (seems NVIDIA uses a new way to identify PhysX runtimes versions: the installer file is called PhysX_9.04.08_9.09.0408_SystemSoftware.exe). This new version is mainly an update release for the game Cryostasis.
You can download the latest PhysX runtimes here: NVIDIA PhysX System Software 9.09.0408 – 39.2Mb.
If you have a GeForce 8+, you can enjoy PhysX hardware acceleration (via CUDA). With all other videocards (GeForce 5/6/7, ATI Radeon, S3 Graphics, …) only software mode is available.