are you using RB to record something you are listening to like a radio program or streamed music? the old creative card drivers had an option callled 'what you hear'. you should be able to do that if you select one of the audio inputs in the RB options - just open the audio and drivers tabs.

if you are trying to record a vocal on to an existing backing rack you will need to use asio or WAS drivers and set them up accordingly - its fairly intuitive with asio as you'll see what's in and what's out

don't forget, in windows there is a sound setting for your recording and playback options