Hi Justin,

Microphones are analog, microcontrollers are digital. For the microcontroller to make any use of a microphone, the signal from the microphone needs to be conditioned (amplified, maybe offset) before going into an analog to digital converter (ADC). Then the microcontroller can do something with the signal. Then you'll probably want some sort of audio output, which will involve either digital to analog conversion (DAC) or pulse width modulation (PWM).

You can find some 8051 derivatives with built in ADC. You might be able to find built-in DAC. PWM is fairly common.

Do a Google search on "Billy Bass hack" and you'll find a simple example of a microphone/microcontroller project, where the microcontroller is used to record sound and later play it back. Most examples I've seen are based on an AVR part, but it will give you the general idea.

Dennis