CUDA runtime DLLs on WinXP vs. Win7

does an end user need different CUDA DLLs (e.g. CUDA run time, BLAS DLL, etc) whether he is running WinXP, Vista, or Win7? Or are they the same CUDA DLLs on all Windows OS’s? I mean the DLLs that NVIDIA supplies, not our application DLLs. Particularly, are the NVIDIA-supplied CUDA DLLs that are for Win7 backwards compatible with Vista and XP systems?