I had this same problem with my machines... 2 were running 98SE and the other two were XP Pro. All the machines could see eachother, but the XP machines could only access the XP machines and the 98SE machines couldn't access anything.

I fixed it by running the XP wizard on the XP machines and at the end of the wizard it gives you the option to make a floppy with that wizard on it. I did so, and ran the wizard on the 98 machines. After completion of the process, all was well on my network. I don't know if you've tried that yet or not, but hopefully this helps a little.

DW