Microsoft's drivers are there as a matter of convenience. It allows the OS to recognize most hardware, thereby eliminating the need to install proprietary manufacturer's drivers from CD. You can safely remove the reference drivers from the directory. By removing, I don't mean deleting, I mean to rename them. For example, rename it to something like nv4dsp.dll.MS. There are also some .ini files that reference the appropriate library files. If they are gone, when you reboot your computer, the hardware wizard will load up and try to find the drivers (as defined by the .ini files). When it can't, it will prompt you to insert a disk containing the driver set.