You know diagnosing a problem or helping in a 'how to' is far easier if the poster gives information about the hardware etc; The question is a bit lacking in detail, what internal mic ?
The more informative you are the easier it is to help.
System Manufacturer/Model Number DIY OS Windows 7 home premium x64 CPU AMD FX-4100 AM3+ 3.6GHz 12MB Black Edition Motherboard Asus M5A97 Pro Memory Crsair vengeance 12Gb DDR3 1600MHz CL9 Graphics Card Asus GTX 560 1GB Sound Card Realtek onboard Monitor(s) Displays Hanns G 1680x1050 native
PSU OCZ StealthXstream II 500W Hard Drives OCZ 128Gb Petrol ssd
2x500 Gb Samsung Internet Speed 8Mb or better
Hello, I guess you're using Windows 7 =)
On the taskbar, near the clock, you can see an icon with a speaker emitting sound waves on it, right click on this, recording devices and then, find the microphone that is integrated, then disable it.