Right click My Computer ----> Properties--->Device Manager--->click the + next to 'sound, video and game controllers'
That will show the basic soundcard you have. In my cast SB Live! on this PC.
Or download a program such as Belarc Advisor or Sandra and that will scan your system and tell you
Open up you PC and take a look at the card and see what it says on it. This is not an option with on-board sound.