Hi and welcome to SF.
I'm not sure if you meant the playback devices or the recording device. But here is a possibility for the recording device :
In Windows 7 you can set two device : a recording device and a communication device. To do so, right-click on the speaker icon in the notification area then, "Recording devices". Right click on the Microphone entry and choose "Set as default recording device" or "Set as default communication device". If you chose the recording device for the microphone, select another device, right click then set it to the communication device.
Hope it helps.