I was up and running in five minutes using the XP networking wizard. XP's wizard made a floppy for me to install on the Win98 machine. I ensured that both computers had the same workgroup name and activated FILE AND PRINT SHARING on both.
I was able to share out the hard drive and ZIP drive on the old computer and map them to the XP computer. I also shared my printer to the Win98 computer as well as the Internet connection. It was so easy that I am kicking myself for not doing it earlier because I used to have to wait hours for my kids to get offline and vice versa. Now we can both be on at once!
One thing I didn't see mentioned that you might have forgotten. When you installed the NIC card on the Win98 computer, it comes with a cable that you are supposed to attach to the motherboard from the NIC. Did you do that?