I have a postgresql 8.3 db set up on linux box, together with a user postgres The pg_hba.conf reads
local all postgres ident
Are you sure you did restart or reload of PostgreSQL after pg_hba.conf change?
If yes, type this command from postgres system account (shell):
psql -qAt -c "show hba_file" | xargs grep -v -E '^[[:space:]]*#'
If this will not help - show us output of the command.