You cannot achieve this from the control panel. Only if the application itself allows you to select audio source in it's settings. Maybe there is a 3rd party program that can do this but I doubt it. Maybe someone else can reveal some way.
No it's a desktop. That's what I have... a good internal one. Maybe I misunderstood... now that I'm re-reading the original post, I don't know what he meant by a "USB" sound card... did he mean internal PCI or some external sound card?
Anyway you might be able to switch back and forth by right clicking on the desktop and selecting personalize, then sounds, I don't know if it will show options for more then one sound card or not, because I've never seen a setup like that, but it's where I switch my output from my computer speakers to Hdmi output for my HD TV.