XP has as it's default workgroup name - MSHOME
Win98 has a default workgroup name of - WORKGROUP
I had some bother trying to convince XP to change it's name to WORKGROUP when I added an XP PC to an existing network. I would therefore advice running the network wizard and create a floppy on the XP machine, then insert the floppy and run it on the Win98 box. That should see you up and running.