[Samba] subnet machines seen on net

[Harland Christofferson]

i have a network i use for code development branching off of the 
corporate intranet.  the topology is:

    +---------------+   +-------------+
    | 192.168.1.100 |---| 192.168.1.1 |
    +---------------+   | 10.20.0.0   |
    engineering3a       | 10.20.1.158 |--- to/from intranet
    wkgrp: speg         +-------------+
                         engineering3
                         wkgrp: speg

on the intranet, engineering3a and engineering3 are seen by other 
machines that have access to the workgroup speg ... i only want engineering3 
NOT engineerting3a seen on the intranet. also, when i ping engineering3 
from another machine on the intranet, it resolves 10.20.0.0 as the 
ip address NOT 10.20.1.158. furthermore, when i ping engineering3a 
from a machine on the intranet, it resolves 192.168.1.100. i don't 
even want engineering3a to be seen on the  intranet. 

what is amiss in my configuration of samba?