There is a known problem in Win98/ME with the built-in 3com network card. Go into the BIOS and disable it in the Integrated Devices and your audio should work fine. You can still purchase another PCI network card and it should work fine.

To get into your BIOS, hold F2 when your computer first turns on (or after a restart), go to Integrated Devices, and disable your On-board LAN. Save settings & exit.