Unable to use inbuild microphone

Hello,
im usin a compaq presario v6000 laptop which has an inbuilt microphone. i have windows xp installed on my laptop.
when i try to have a voice chat wid someone, i can hear the person at the other end however my voice is not transmitted to his end. can i get some help on how i can get my microphone to use?? if the problem persists due to lack of drivers, can u plz suggest which drivers to install??