TKP went to find some external microphones for this tablet only to have a few retail salespersons to tell him that there is no way to use an external microphone.   

The built-in microphone, he was told, is the only option for use on the Tablet. 
or NOT. 

Turns out the built-in microphone is fine ( its the tiny hold next to the 30pin interface port on Galaxy tab 10.1)  
 but if you want to use an external headset & microphone at times instead of the built-in microphone 
you just need a headset/microphone combo that has a SINGLE 3.5mm jack interface rather than the separate lines for the headset and microphone output. 

You can buy a headphone like this: 

GE 98974 Voip Stereo Headset
 

Or get a adapter like this:

Headset Buddy: PC Headset to 3.5mm Smartphone Adapter::