[brustler]

I use a ViewSonic 22" LCD with my Mini thus I don't have the built-in camera and mic. So I use my Sony MiniDV via Firewire. The camera's mic won't work with Skype. Neither will a mic plugged in the mic jack of the Mini. Does one cancel out the other?

[retcynm]

Under the Audio tab in Skype preferences, you should be able to select the Sony camera's mic as the audio input for Skype (as long as the Sony cam is plugged in to the Mini).
I'm also pretty sure that the audio input port on the Minis is a line-in port, not a mic port. You would need to either get a Griffin iMic to have a mic-in port, of get a USB Mic.
The microphone on the Sony camera should work, though.