OS - Vista Ultimate 32-Bit

Realtek HD Audio
Driver Version - 6.0.1.5443
Audio Codec - ALC885

Problem - Well the problem is when I'm recording a song(in Audacity) with the background music playing in Audacity , the music also gets recorded and it ruins the whole recording . This should not happen as I'm using headphones while recording. The same problem used to happen when I was using XP . But I got rid of that from the Volume Control of XP. But in vista there are hardly any options to customize the sound mixer .

So in short I want that when I record the song there should be only vocals and not music. Please help!!

You can always try to download new versions of your driver, I looked up Realtek HD Audio codecs and there seem to be new downloads available updated the 31'st march 2008 right here

Just select the right amount of channels and download the latest versions.

Also in Vista, the soundmixer lets you select settings by device driver and applications. Maybe you should look for settings of the application Audacity, the application should be listed in there when it's opened and perhaps you'll find more settings there.