ODBC and unknown i.p.

I am using postgres 7.3.1 on a slackware linux server and psqlodbc.exe
version 07.02.0005. I am a novice at both linux and postgres
administration.  We are in the process of converting from a SCO unix server
with Ingres1.2 database to the aforementioned linux/postgres server. Our
application is distributed to customers around the world and uses ODBC
connections in VB applications. With our old system, we only had to be able
to connect to the database server through ODBC and user/password security.
It appears that there is another level with postgres--namely the addition
of entries into pg_hba.conf, which include the i.p.and subnet. Since this
is a distributed application, we have no way to know in advance what the ip
and subnet of users at a given site will be, much less when a customer
changes his local network. I tried a VB app without an entry in pg_hba.conf
and failed, but succeed when the entry is added.

Is there an easy way around the pg_hba.conf problem? If not, has anyone who
has dealt with this issue have any suggestions?
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