Harmon Kardon no longer list the manual for your speakers but going by the reviews they were out in 2002.
They were decent and unless they're dieing on you they shouldn't be a problem, having trouble with volume on aging spealers usually means it's time to go shopping.
If that's the AC'97 then you have the same on-board sound I do and your drivers are two years out of date.
Latest here :
http://www.download.com/Realtek-AC-9...-10238712.html
(WDM means windows driver model)