Microphone setup in Windows XP

Microphone setup in Windows XP

On Windows XP, while on the speech control panel, I see that my voice is recognized by my computer when the Microphone is not connected (where is the voice input in such a case, I am using Thinkpad T400) and when I connect the microphone in the micro-phone jack, the voice recognition turns off. I want the opposite behavior, what should I look for and be careful about as not to do any mistakes?