I'd be amazed if the problem is your soundcard. The best onboard sound is about a generation behind the SB Live, and the chipsets loaded into HP's are a generation or three behind that.
If volume is the problem, my money says that one of your volume controls is limiting the peak volume. Windows has twenty or thirty of these controls (I exaggerate only slightly) and one can cap the output of your sound system.
Dig through them, starting with the master volume control and working through all of your media players, and make sure they are all turned up to eleven. Then use the volume dial on your speaker, or through your keyboard if you have hotkeys, to control the volume.
BHD