D630 will not recognize external mic

Hello,

I am using a Latitude D630 laptop (running Windows XP) at work and need to use a sound-eliminating external microphone that I have purchased. However, I cannot get it to work, despite it working fine on my desktop computer.

Here's the situation:
My microphone/headset comes with the standard green and pink headphone jacks. I have plugged the green one into the headphone jack and the pink one into the microphone jack. When the mic is connected, the SigmaTel "Audio System Event" pop-up appears and I select microphone from the list and click OK. However, when I choose external microphone (or line in, which I have also tried selecting from the initial pop-up screen) in Camtasia, nothing is detected. The internal mic works, but it does not deliver the quality I want. Do I need to shut off the internal mic somehow? I have gone into the sound properties and muted it, but I am still unable to use my external microphone.

I have also gone into the audio settings from the control panel, but have not been able to find anything that works there either. In fact, the "Test Hardware" tool in the audio properties window doesn't detect the microphone either.

Is this a driver problem? If so, could someone point me to where I can download it?

Thank you