Win 2000&98 network blind

I’ve got 2 Win98 and 1 2000 Pro installed at my home peer-to-peer network. They are connected with 3C509b -cards and all belong in the same workgroup. Protocol is TCP/IP. The two Win98 PC:s work fine together but Win 2000 can’t see either of the 98’s and vice versa. Neither does ping go trough. HW is tested and ok. (Worked with NT4.0Wks) I’ve tried newer drivers, NetBEUI, IPX/SPX, changing HW (desperate:), uninstall/install etc. Network properties indicates that everything is ok but nothing still does not work. Win 2000’s own netaddress answers to ping as it should. Tell me, please, what to do next?