Monti,
Hmm, Very interesting problem. Did you install the Sound Drivers from the CD that came with the Motherboard???? If so then try uninstalling those and install from the lastest version available at the website. (some CD's auto install the wrong drivers)
Looking at the website I notice there are "Different" drivers
for 98 and 98SE (seems unusual) so make sure you get the right ones.
Also I'm wondering, did you install the VIA 4 in1 drivers right after you installed Windows and BEFORE you installed the sound drivers?
Let me know, I'll check back to see what happens.
SHawk