Dell 1545 audio output works except input mic (internal)

[inspiron01]

Computer: Dell 1545
OS: OSX 10.6.4
Graphic: GMA 4500
CPU: Intel Pentium Dual-Core 2.16Ghz
RAM: 3GB DDR2

Issue:
My audio (output) works perfectly right after the installation.
But my built-in mic is not working as well as volume control.

Under Sys Pref>Sound>Input> my built-in mic is not listed.

I've been searching for this driver for a while, hope someone can help me. thanks