Direct Connection and Network Neighborho

I have 2 Hp’s n/w peer to peer with a hub. the other site has 3 Compaq’s n/w peer to peer with a hub. I have a 700ft serial direct connect between the 2 sites. The Hp with the serial can see everyone on both sides. The second Hp can only see the Hpserial. Protocol is Netbui and tcp/ip. Can’t ping to or from 2nd HP to other site….What’s up??