Here's my quick test of on board / PCI sound card quality.
Open Wave Lab or any good quality wave editor.
Disable the Mike input
Turn up the line in with control panel ( Creative has it's own mixer )
Don't plug anything in!
Put the software in Record mode and observe the meter and Phase scope.
You'll soon see if the system has a terrible noise floor. Most do.
Some you'll see little spikes from hardware and DPCLAT stuff.
I was pleasantly surprised that my Asus laptop was dead quiet and that's a friggin, realtech!