One speaker, the right is louder. Is there a way to adjust balance?

Yes, there is. In Win 7 you can right-click on the little speaker in the system tray.Click on playback devices. Double click on the speakers you are using and you'll see the speaker properties. Click on levels and you'll see volume and balance.
In Win XP, you can click on Start and programs and either multimedia or accessories and multimedia (I'm doing this from memory). That has the sound controls.