Mixing library versions

I'm currently experimenting with the Debian packaging of 6.4.

The question arises of how to handle the change in library versions from
1.0 to 2.0.  It has been suggested that I should keep libpq.so.1 around
for the benefit of those who need to communicate with an older database
server.

Is it possible to use libpq.so.2.0 to query a remote database whose
server is running PostgreSQL 6.3?  What would be the consequences of
using libpq.so.1 to query a 6.4 server?

-- 
Oliver Elphick                                Oliver.Elphick@lfix.co.uk
Isle of Wight                              http://www.lfix.co.uk/oliver              PGP key from public servers; key
ID32B8FAA1                ========================================    "Lo, children are an heritage of the LORD; and
the      fruit of the womb is his reward."        Psalms 127:3