I have played around with your suggestion for some time now, but can't seem to turn off the onboard microphone and speakers, without also turning off the skype microphone and earphones.
In fact, when skype is on, my laptop makes all kinds of loud noises when someone calls. Sort of embarrassing. I suppose I will figure it out as I get more familiar with Skype, which, by the way, is a great program. Sort of in-between a land-line and a cellphone. For those of us who don't have cellphones, this is a distinct plus.
I will keep at it, but meanwhile other suggestions are appreciated.