It sounds to me like "What_does_this_button_do?" has got it about right.
Downloading the latest drivers for your motherboard's chipset might well do the trick. These are usually quite easy to install once you've downloaded them.
You might also want to just make sure that your mobo's on-board sound is still enabled in the BIOS. Your motherboard manual will show you how to do this. If you don't have the manual, you should be able to download it from the manufacturer's website.
Just one thing - how come you went back from Win XP to Win2K? Seems a bit of a retrograde motion to me!
