What type of sound card is it? Is it a laptop or desktop? What version
of Ubuntu are you running? Do you have any other apps hogging the
sound card (such as Firefox with Flash open, or Skype)? Can you try
going to the mixer preferences and adding in any additional microphone
related controls or switches, and then adjust them. You could also try
killing the pulseaudio process (if you're using Ubuntu 8.04) as this
sometimes gets in the way. The other thing you can try is using a
different audio recording application. Audacity is good.
Chances are you don't need to install any drivers. Ubuntu comes with
drivers for pretty much everything (more than any other OS at any
rate) pre-installed.
Cheers,
Al.