Windows 7 has a new Volume Mixer feature & Volume Control options. The key improvements to this feature are better graphic displays & the ability to control the sound levels of all the applications which call for audio support from Windows 7.
This new mixer effectively lets you control the volume for each application separately. To access it, click on the speaker icon situated on the right side of the taskbar.
Next click on Mixer to open the Volume Control window.
Here you can control the volume for you running applications which are currently calling for Windows Audio support. For instance if you are listening to an YouTube video on in your Internet Explorer, you might want to soften the system sounds down a bit.
You can also control the overall level of sound on your PC. Move the sliders up or down to raise or lower the volume of your speakers, Windows sounds, or other sound devices or programs listed in the Volume Mixer. To mute the volume, click the Mute button.
Right clicking the speaker icon, will give you more Volume Control options.
To get the Windows 7 Volume Control in Windows Vista, you might want to check this out.