Apart from enabling sharing have you shared anything? i.e if in file manager you right click on my documents and select properties have you been to the sharing tab to activate sharing for that resource.
The win 98 can't see the network thinky is also happening on my home network which is very similar to yours - haven't had the time or inclination to look into it but I suspect it's something to do with win98 not being that network friendly as XP.
hth
amofw