whole bunch of realtek fixes

http://windows.bigresource.com/Win7-Realtek-Audio-Drivers-and-stereo-mix-sound-problem-L6OJYH3m.html

Or to summarise - update your sound card drivers with the appropriate drivers for your operating system, and don’t expect Vista drivers to work on Windows 7, especially not on 64 bit Win 7.
There’s additional information about that in the Audacity wiki: http://wiki.audacityteam.org/wiki/Updating_Sound_Device_Drivers