pg_hba.conf woes

Hi,

    I installed postgres v3.4 but cannot connect to it, as I always get
user authentication failures. I've already wittled my pg_hba.conf down
to

host         all         127.0.0.1     255.255.255.255   trust
host         all         192.168.51.0   255.255.255.0         trust

which should cover our local network and the local host. I cannot even
connect as postgres from the local host. So what am I doing wrong?

Any hints greatly appreciated!

Adriaan