Well, before buying a card see if it says "supports Win98". If it doesn't, look at the manufacturers website for Win98 drivers for that specific card. If it doesn't, Google for the drivers.
Windows 98 Second Edition supports USB, although I am not sure it will work with any card, it should. Do you know if you are running Win98SE?
TheMajorMMX - Intel P200 MMX @ 225Mhz - V-Tech (PcPartner) Baby-AT mb w/ Intel Triton TX chipset - Nvidia Riva TNT2 M64 w/ 16MB - 256MB M-Tec SDRAM - Still running.....