The only major change in the CUDA 2.1 Beta Toolkit is improved OpenGL interoperability by only copying shared buffers through the host memory when CUDA and OpenGL are running on different GPUs. The CUDA 2.1 Beta SDK brings smokeParticles for volumetric particle shadows samples and a cutil_inline.h header file.
This beta release isn't particularly interesting and what it also lacks is any support for OpenCL layered atop CUDA. Though CUDA 3.0 is already being worked on for introduction in 2009.
To download the 2.1 beta of the CUDA Toolkit or SDK, visit this page. The latest NVIDIA Linux driver at this time remains 180.16.