Sounds like you're having an IRQ conflict.
Windows 98 is notorious for its poor assignment of IRQ addresses. This could be why you didn't have the problem in Windows XP, which is by far more adept at doing so.
To solve the problem, check your motherboard manual. Somewhere in there should be a chart explaining exactly which PCI/ISA slots use which IRQ addresses. Some are slots share addresses, which is where Win98 runs into problems. Using the chart, figure out which device(s) are conflicting with your sound card, and then move the cards around to an appropriate configuration.
If you don't have a motherboard manual, or don't know what motherboard you have (and as such, can't get a manaul online) you're going to have to "plug and pray" *grins*. Just swap your sound card into a different slot, start up the comp, and see what happens.
Hope that helps!