The Tahiti/Monterey requires a line-level input.  A microphone alone produces 
a signal that is significantly lower than this. 

Plug the microphone into a mixer (with line-level outputs), a microphone 
pre-amp, or a tape deck with microphone inputs and a line-level output, 
and then connect that to the In on the sound card. 

A mixer (although pricier) is the best solution, since it has a built-in 
pre-amp and allows you to control the tonal quality.  Also, you may mix 
multiple mics and other sources like synthesizers with independently-
adjusted levels and EQ settings. 

Note: As always, caution should be exercised with Audio equipment not to
  overload the various inputs on the card to avoid possible input "frying".