Most of the PC cards I've seen have been PCI cards. If you don't have a PCI slot you may be able to find a card for an older kind. A USB card may need a "BUS Enabled" slot, and lots of PCs with a half dozen or so PCI slots only have a couple that are BUS enabled. The "System Requirements" info for the specific device you might get would be your best guide, used of course with the User Manual for your machine.

I haven't heard of any particular problems with Win98 and USB2, but haven't had a Win98 machine up for quite a while. Again, any card you get to plug into your machine should give you a list of requirements and compatible hardware/software. Nothing specific shows up in the generic:

General USB Troubleshooting in Windows 98, Windows 98 Second Edition, and Windows Me: KB article 263218.

The article contains links to about 50 additional KB articles about specific problems you might encounter with USB. About 14 of them are specific to Win98SE, with about twice that many specific to WinME. Too many to research second hand, but you may be able to spot something with your own firsthand knowledge of your system. Most of the linked articles appear to deal with problems with specific devices you might connect to your USB port, rather than with problems in setup of the machine itself.

If you have more specific concerns, you can go to:

Advanced Search for the Microsft English Knowledge Base.

I'd suggest selecting Windows 98 as the "Product," if that's what you've got, and something simple like "USB" for what to search for. Generally, down at the bottom, check the first three "where to search items." In rare cases you may need to go into the TechNet and MSDN (Designer Network) but these deal more with programming problems and server management than with user information.

John