This is a tutorial about how I use Guitar Rig 3 as a vst plugin for audacity.
Note:
I maybe forgot to mention, once you enable vst plugins in audacity you have to move the .dll file in Guitar Rig into Audacity. Copy and paste it from c:/program files/native instruments/guitar rig 3/VST plugins into c:/program files/audacity/plug-ins.
Hope that helps.
Update: If you have questions see my reply to this video:
http://www.youtube.com/watch?v=CXaARK_l31g