I looked a lot on this and likely found your answer. It uses a non-standard microphone plug. Its a technical answer, you will need to take a look at this link.
Your particular thinkpad DOES use a combined mic/line input...
The excerpt is below, but look a the link.
Best of Success!
When attaching an external microphone to the ThinkPad, it does not work. If the connector is removed part way out, then it appears to work.
Any ThinkPad where one is attaching an external microphone to use instead of the built in microphone .
NOTE: Not all models have built in microphones. Refer to your User's Guide for your particular ThinkPad.
If you are using a condensor microphone, then it must provide own power, either through the use of batteries inside of the microphone, or through the use of an AC adapter. Pulling the connector part way out, the external microphone is no longer disabling the internal microphone which gives the appearance of the external microphone working.
Following is an explanation of the ThinkPad microphone connector:
1. Some ThinkPads use a combined microphone or line input connector. Basically, the microphone jack is a 1/8" (3.5mm) stereo mini-jack, but differs from "standard" jacks in two ways:
a. There is a second contact that touches the ground ring when a microphone is connected. The purpose of the second contact is to ground out the internal microphone when an external microphone is plugged. This second contact should be of no consequence for external microphones and their connectors.
b. There is a metal ring on the outside of the connector (visible from outside the ThinkPad). This connects to +5V through a 2.7 kOhm resistor.