Older computers (assuming its old because you are using windows 98) have a known draw back when it comes to IRQ assignments on PCI slots. When you installed your wireless NIC was it in the slot near your sound card? You may want to move either the NIC or the sound card to another PCI slot on your Motherboard. Usually adjacent PCI slots share IRQs. If you could get a free PCI slot between your devices you should be set. If not, then you may have to juggle between the slots to see what works. Some devices share nicely and some dont.
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