XP PC’s Do Not See 98 PC’s

I have a small home network consisting of 4 PC’s, 3 run XP and 2 run 98SE. (one is Dual-boot but same NIC) All XP PC’s can see each other and 98’s can see the XP machines but not vice-versa. Also, note that the 98’s can see each other. I have installed IPX/SPX on each one. All are in the same workgroup, configured accordingly connected by a passive hub. Previously, I was able to see both configurations without difficulty. Any ideas?