[DrBeast]

Yes, you'd have to find it in the BIOS menu and enable it. You access the BIOS upon boot usually by pressing the Delete key (though some BIOS require another key, watch the screen closely upon boot and you'll see a "Press [keyname] to enter Setup" or similar message.

HOWEVER...before enabling it you'll have to disable the other sound card! Uninstall the drivers etc. Worst case scenario (meaning you don't have an on-board sound chip), you just reinstall its drivers.

Here's what to do: upon boot, enter BIOS. Check to see if you do have an onboard sound chip. If you do, mark down its type. Now exit BIOS without saving. Do a google search for "sound chip type drivers", download the latest drivers. Now, uninstall your current sound card's drivers. Shut down the PC, remove the sound card. Fire up the PC, enter BIOS, enable on-board sound, bypass the whole "Windoze has found a new device", manually install the drivers you downloaded. That's all.

Note: this is for Windoze XP, I have NO idea how Vista work!