non-line-buffered key input in C?

I'm learning C from a book that uses the getche() function from the
<conio.h> library to get instant keyboard character input from the user.
The preprocessor/compiler (gcc 3.3 on Panther) doesn't recognize the
function nor the library. The getchar() function only works line-buffered.

How can I get a program to accept character input without waiting for
the user to press Return?

Any help would be much appreciated.

Eric