Ensure that the computers are both in the same workgroup.
Check that you can ping the IP address of each PC.
Check that you can ping the name of each computer.
Ensure that you have created shares on each computer as required.
Win 98 uses FAT or FAT32, which doesn't support security other than at Share level, so it is always easier to see shares on a Win 98 PC from an XP PC than vice-versa, as XP uses NTFS which supports file-system security in addition to Share-level security.
Suggest you see M$ site for networking 98 and XP info.
Sd